"Punctuation, grammar, and spelling are not things that only happen to other people."--Terry Pratchett

PLOT
Many writers of fiction labour under the mistaken belief that their stories do not require a plot, without a plot, what you have is a fragment, or perhaps a scene in search of a story. These scenes can be well-written, even beautifully so, but they are not stories. A story has a beginning, middle, and end. A story has direction; it is going somewhere and the reader is along for the ride. The parts can be broken down as follows:

Beginning:

This is where at least one main character is introduced, along with the setting. It is usually a good idea to describe both characters and setting, so that the readers know who and where these people are and can picture them in their own minds. Writing about characters established on a television show or in other stories does not mean that the author should skip descriptions.
The beginning is also where the plot should be introduced, preferably as soon as possible. The shorter the story, the earlier the plot needs to begin. Try to draw the readers in by starting with something that grabs them and makes them keep reading. Which of these examples would make you want to keep reading?
Blair lay in bed, remembering what had happened that day, how Psycho J. Killer had held the gun to his head and threatened to kill him in front of Jim.
Psycho J. Killer jammed the gun into Blair's temple, gripping his arm so hard that Blair's fingers went numb. "I'll kill him, Ellison!"

Middle:
This is where most of the stuff happens. This is where the characters are developed along with the plot, where we get the details, the conversations, the relationships, and the clues. In a longer story, this is where you can slow down and show the readers what you want them to see at a pace that you set. This is where you build up the readers' expectations, make them wonder and guess, keep them in suspense. This leads to...
Climax: The climax should be the most exciting part of the story. This is the payoff, the hold your breath or break your heart. In the climax, Jim catches the murderer or rescues Blair from Psycho J. Killer at the last possible moment, or Blair finally has that emotional breakthrough you've been building up to all along. It can be a quiet breakthrough, but the readers have to know that this is what they've been waiting for. It is almost always a bad idea to have the climax happen off-stage. If you go to all the trouble of setting up a murder investigation, showing the readers the victim(s), following Jim and Blair as they question the suspects and search for clues, then toss an offhand, "Oh, by the way, Chief, while you were in the hospital, the murderer confessed: the butler did it," your readers will not be happy or satisfied. They may form a lynch mob.

End:

The end is where everything winds down, where loose ends are wrapped up, hugs are given and received, and bad jokes are made. This is where you tell the readers what happened after all the excitement was over. If you feel like it. It is quite possible to simply end the story directly after the climax and never tell the readers another thing. The end can be as abrupt or as long as you wish, but it is advisable to avoid boring the readers with too much information or confusing them with too little. Though not always possible, coming up with a final sentence that's just as good as the opening sentence is a Really Neat Thing.

EXPOSITION
You all know Mr. Exposition. He's the character who says, "Well, Jim, as you know, the Chopec are a people who live in Peru but occasionally take ocean voyages to Cascade in order to seek out the heads of corporations that are destroying their lands." His is a thankless job, that of explaining to the readers who a character is and exactly what is going on, or of giving background information. Sometimes, she is Ms. Exposition, or Dr. Exposition, but the job is always the same. In bad writing, Mr. Exposition has no other purpose as a character than to dispense information. He is not really a person at all, but a walking encyclopaedia. In the worst writing, Mr. Exposition is not a character, but the writer himself, giving the readers lots of information in blocks of not very interesting prose. This is also called info-dump.

Info-dump is to be avoided whenever possible. Yes, some information does need to be given straight out, but a good writer tries to find an interesting way to do that. MOST information should be woven into the story in such a way that the readers are not consciously aware that they have been sucking it into their brains. It is more fun for the readers to believe they have discovered such titbits on their own than to have info-dump forced upon them in large, unpalatable chunks. This leads us to the most important rule in fiction writing:

SHOW, DON'T TELL

No fooling. This is serious. Don't TELL the readers what is happening or what the character is feeling, SHOW them.
Bad writer: Blair really felt terrible about lying to Jim.
Good writer: Oh, God. Blair put his head in his hands, tears stinging his eyes. How could he have lied to Jim?
Bad writer: Jim was so angry that Blair was afraid.
Good writer: Jim grabbed the front of Blair's shirt and slammed him into the wall. Blair fought to breathe, his heart hammering.
Draw the readers in, make them a part of what is happening. Try to avoid "While you were gone" summaries of scenes you should have shown. Don't tell them, "Earlier that day, Blair had gone to the university and run into Suspect J. Student, who had said something incriminating that Blair now waited anxiously to tell Jim." SHOW the scene at the university, show Blair's conversation with Suspect and his subsequent anxiety. Get them involved, give it dramatic impact, show them What's Happening Now.

CONTINUITY

Auntie Continuity (Those who pronounce "aunt" as "ant" will get the joke. Those who pronounce it properly may not.) has a demanding job. She polices plots for holes, and descriptions for unexplained changes. She is the one who notices when Blair's beautiful blue eyes suddenly become green, when the loft magically acquires an extra bathroom, and that Lefty could not possibly have done it because in Chapter Three, Jim said the guy was right-handed, and Lefty is missing that particular limb. Writers who do not have an Auntie Continuity will have to do the job themselves. Or find good beta readers to do the job for them.

POINT OF VIEW

There is one basic recommendation regarding point of view: Pick one and stick to it.
This does not mean you have to use one character's pov for the entire story. This does mean you have to use one character's pov for an entire scene. What is a scene? Well, technically, scene is a term used in plays, films, or television. When HMG says "scene", she means a bunch of paragraphs and dialogue strung together between breaks. In other words, a section of your story wherein the action and/or dialogue occurs without a break, and usually without a change of location.
For those who may not know what pov (point of view). Point of view is the means by which the readers see the scene you have written. Point of view is the camera lens through which they peer. While it is possible to use an "omniscient" pov, in which the viewpoint character is the author (also known as God) and therefore knows everything that goes on in every character's head simultaneously, it is preferable to use the pov of one character per scene. This means that the readers see only what the pov character sees, and know only what the pov character knows. This also means that the readers are placed directly into the mind of the pov character and can see his thoughts. The writer must remember that, unless he is telepathic, the pov character cannot hear the thoughts of another character; and that, unless he is gazing into a mirror, the pov character cannot see himself. Switching back and forth from one character's head to another as the scene progresses is confusing to the readers. Don't do it. Oh, and don't do the mirror thing, either, it's a dreadful cliché. If you need to describe how the character looks, use someone else's pov in the next scene or rethink whose pov you want to use in the current one.
Bad: Blair looked at Jim, wondering what was going on in his partner's head. Jim glared at him and he blushed, his blue eyes looking away. Was Jim mad at him?
Worse: Blair wondered what was going on in Jim's head. Jim glared at Blair, and the kid blushed, his blue eyes looking away. Was Jim mad at him?
Good (Blair's pov): Blair wondered what was going on in Jim's head. Jim glared at him, and he looked away, his face burning. Was Jim mad at him?
Good (Jim's pov): Blair was giving him the puppy-dog gaze again. Forget it, Sandburg, you're not getting out of this one that easily. Jim glared at him, and the kid blushed, blue eyes sliding away.
Final note. Unless you are using the omniscient pov, never use any variation of "Little did he know". This includes, "He would soon wish." If the pov character doesn't know it, right now, you can't say it. And if you can't find some other way to build suspense,

TENSE PERSONS

Two basic rules together:
1. Stories are best written in the past tense. Scripts are written in the present tense. If you are writing a script, do it that way and you will be fine. Stories written in the present tense almost never work. Use the past tense. Use it all the time. No arguments.
2. Stories are best written in either 3rd or 1st person.
Occasionally, a writer will take it into her head to write a story in the second person. This is a strange and terrible thing. Never, ever do it. Use third person, "he, she, it" or first person, "I". It is possible to mix the two, if you draw clear lines between scenes using first person and scenes using third, but it is not easy and often looks badly put together.

DIALOGUE

Ah, dialogue. Sit back and relax, this will take a while.
1. Know your characters. If you have invented your own characters, you may have them speak any way you like, as long as it sounds natural for the time and place in which they exist. If you are using someone else's characters, take care to use them properly. Study them. Learn their speech patterns. If you are writing a contemporary story, the characters will use contractions when they speak. Listen.
Bad: "Jim, you are not communicating effectively," Blair said. "I cannot comprehend your meaning."
Good: "Jim, man, you're not making any sense," Blair said. "I can't understand what you're talking about."
2. Every time someone different speaks, start a new paragraph.
Bad: "Jim, are you sure?" Blair asked. "Yeah, I'm sure." "Really?" "Yes, Sandburg, really."
Good:
"Jim, are you sure?" Blair asked.
"Yeah, I'm sure."
"Really?"
"Yes, Sandburg, really."
3. Make sure the readers know who is talking. But don't overdo it. If only two people are talking, you need only identify them occasionally, so the readers can keep them straight. If more than two people are talking, you need to tell the readers who is saying what when. Examples:
Two people:
"Jim, I don't get it," Blair said.
Jim raised an eyebrow. "Don't get what, Chief?"
"This case, man. It doesn't make any sense."
"Here it comes. Sandburg, what part of 'case closed' don't you understand?"
Three people:
"I don't get it," Blair said.
Jim raised an eyebrow. "Don't get what, Chief?"
"This case, man. It doesn't make any sense."
"Here it comes," Simon groaned. "Sandburg, what part of 'case closed' don't you understand?"
4. "Said" is a perfectly good word. It tells the readers what they need to know. It is not necessary to rack your brain trying to find a substitute for "said", or for "asked". It is not even necessary to use "said", except to tell the readers who is speaking (see 3), or to provide a pause between dialogue. Use words other than "said" only when you find it necessary to describe to the readers how the words are being spoken because the dialogue itself does not make that clear. And please remember, if you must use "replied", that your character can only reply if he is answering a question. Examples:
"Don't do that," Blair said.
"Don't do that," Blair pleaded.
"Don't do that," Blair ordered.
"Don't do that!" Blair screamed.
5. Punctuate, punctuate, punctuate. Here's how, in six easy lessons.
A. When you describe how the dialogue is spoken, that description is part of the same sentence as the dialogue. When the description comes after the dialogue, end the dialogue with a comma, and put a period after the description. When the description comes before, put a comma after the description.
Bad: "I don't want to." Blair said.
And Blair said. "I don't want to."
Good: "I don't want to," Blair said. Or Blair said, "I don't want to."
Good 2: "Blair, you are the most beautiful man I have ever seen," she said. (Notice "she" is not capitalized here, because it is part of the same sentence as the dialogue.)
B. If the dialogue is a question or an exclamation, the same rule applies to the description.
Example: "Leave me alone!" Blair screamed.
Or Blair screamed, "Leave me alone!"
Example 2: "What are you doing?" he asked.
Or He asked, "What are you doing?"
C. If what comes before, after, or between the dialogue is not a description of how the words are spoken, it must be treated as a separate sentence, and the first word must be capitalized.
Bad: "You can't do that," Jim walked away from her.
Good: "You can't do that." Jim walked away from her.
Or "You can't do that," Jim said, walking away from her.
Bad: "I like that," the anthropologist smiled, "It feels good."
Good: "I like that." The anthropologist smiled. "It feels good."
Good 2: "What is that?" She peered into the box, and screamed, "Oh, my God!"
Or (since it should be obvious from the dialogue how she is saying it) "What is that?" She peered into the box. "Oh, my God!"
D. Don't overuse exclamation points! Never, ever do this! If you do it too often, the readers will cease to become excited by them! Use them only when you have to! And never use more than one!!!
This also applies to using bold, italics, or underlining for emphasis. Too much, and they no longer mean anything.
E. Dashes and ellipses. Ellipses are used when the dialogue is trailing off. If the dialogue trails off, then picks up again, use three periods. If the dialogue trails off without an end, use four periods. Dashes are used when there is an interruption, or a hesitation. Example: "But, Jim," Blair said, "I really thought you should know about...." Oh, what was the use? Jim wasn't listening.
Example 2: "Jim, I--I can't." Blair looked away.
Example 3: "Jim, look out! It's--"
As with exclamation points, be careful not to overuse dashes or ellipses. Most of the time, your characters should be able to finish their sentences.
F. If you break your dialogue in the middle of a sentence, do not capitalize the first word when you resume.
Example: "The problem," Jim said, "is that we don't know her."

Internal Dialogue:

This is what you have when your character talks to himself in his head. There are various acceptable ways to indicate internal dialogue. The most common is italics.
Example: Why am I so stupid? Blair thought. How could I have told Ellison he was a throwback to pre-civilized man?
Example 2: Why am I so stupid? Blair shoved his hair back. How could I have told Ellison he was a throwback to pre-civilized man?
You can also use quotation marks, either double or single.
Example: "Brilliant, Sandburg," Blair thought. "You just drove your dissertation subject out of your life in under five minutes."
Example 2: 'Sandburg.' A wicked grin spread across Blair's features. 'It's payback time.'
Using quotation marks requires treating the internal dialogue as though it were spoken out loud, with the same rules of punctuation and capitalization, and the ubiquitous "he thought" generally inserted somewhere in order to make it clear to your readers that the character is not, in fact, speaking aloud. Italics do not necessarily require "he thought", and can be intermingled with non-italicized actions, as shown.
It is not necessary to use any of the above to indicate internal dialogue. Quotation marks can be confusing, and the overuse of italics becomes not only annoying, but meaningless. Also, in these modern times, stories in html or e-mail often lose their italics (not to mention bolding, underlining, or any other fine and fancy indications of emphasis you may use). It is perfectly possible to indicate internal dialogue simply by changing tense, by wording the internal dialogue as you would spoken dialogue, or by changing from third to first (or second) person.
Example: Why am I so stupid? Blair shoved his hair back. How could I have told Jim he was a throwback to pre-civilized man?
Example 2: Why was he such an idiot? How could he have done that? Man, I've had it, now. Ellison's never gonna work with me. I'll be lucky if he doesn't rip my head off right here.
Example 3: God, he was so stupid! First, he lied to get Ellison in here, then he told him he was some kind of cave man. You idiot, Sandburg. You've completely blown it. Now what are you gonna do?

NAMES, PRONOUNS, DESCRIPTIVE PHRASES

As with "said", names are perfectly acceptable words. They are useful, as they allow the readers to know who you are talking about. It is not necessary to find new and wonderful descriptive phrases to identify your characters at every turn. Generally, their names do the job.
Pronouns can be confusing, especially if everyone you are talking about is of the same gender. If the pronouns are not enough, use the characters' names to identify them. If the sentence is still confusing, rewrite it. If this is not possible, then try a short descriptive phrase, but only as a last resort. The rule is clarity above all else. If the readers can follow the action, you are doing your job as a writer.
Bad: He grabbed his arm and slapped him. He struggled to raise his bound hands.
Good: Lash grabbed Blair's arm and slapped him. Blair struggled to raise his bound hands.
Bad: He grabbed his arm, lifted his hand, and slapped him.
Good (Lash's pov): Lash grabbed Blair's arm, lifted his hand, and slapped the struggling man.
Good 2 (Blair's pov): Lifting his hand, Lash grabbed Blair's arm and slapped him.
Bad: He grabbed his arm and slapped him. Lifting his hair away from his neck, he gagged him.
Silly: Lash grabbed Blair's arm and slapped him. Lifting Blair's hair away from Blair's neck, Lash gagged Blair.
Good (Lash's pov): Lash grabbed Blair's arm and slapped him. Lifting the brown curls away from Blair's neck, he gagged the struggling man.
Good 2 (Blair's pov): Lash grabbed Blair's arm and slapped him. Lifting the hair away from Blair's neck, Lash gagged him.
Why are the first examples from Lash's point of view? Because Blair would not think of himself as "the struggling man", now, would he?

FRAGMENTS

As a general rule, sentence fragments are bad things. They are acceptable in dialogue, because people do not always speak in complete sentences. To be absolutely correct, however, fragments should not appear in your narrative.
That said style over rules. Sentence fragments, when employed judiciously, are useful dramatic devices. By this means that sentence fragments should not be used every chance the writer gets, nor should they be an excuse for sloppy writing. They should not be used by any writer who has not proven a thorough knowledge of the rules of grammar.
Example 1: Blair gazed down at the bomb. Oh, God, he had to defuse it himself. How? He didn't know anything about bombs. Taggert spoke in his ear, and he lifted the cover off, slowly, carefully, praying he wouldn't set it off.
Example 2: Blair gazed down at the bomb. Oh, God. He had to defuse it himself. How? He didn't know anything about bombs. Taggert spoke in his ear, and he lifted the cover off. Slowly. Carefully. Praying he wouldn't set it off.

SPELLING COUNTS

It does, too. Incorrect spelling makes reading your story more difficult. It also gives the impression that you don't care enough about your writing to do the most rudimentary checking. If you don't care about your story, why should your readers?
Spellcheck. Make corrections. Spellcheck again. Then read the story to find all those words the spellchecker didn't catch. The spellchecker doesn't know the difference between "there", "they're", and "their", but you do, right? Use a dictionary. When you're done, have someone beta read for you. Someone who knows at least as much as you do about spelling. Okay? Good.

PLURALS, NUMBERS, AND APOSTROPHES

Plurals are, like, really easy to make, dude. Mostly, you just add an "s" to the end of the word. Sometimes, it's "es", but mostly, it's just "s".
Some people think that they have to add apostrophes when pluralizing, especially when pluralizing names. This is not true. To make a name plural, just add that "s" or "es". Like so:
Jim--Jims: How many Jims are there, anyway?
Sandburg--Sandburgs: Blair and Naomi are the only Sandburgs we know.
Banks--Bankses: Simon comes from a long line of Bankses.
The only time you need to use an apostrophe to make a plural is with numbers, and only in numerical form, not written out: 80's, 90's, 100's
You can use apostrophes, or not, with initials or acronyms: How many MA's does Sandburg have?
Speaking of numbers, they should, for the most part, be written out in words.
Bad: 30, 6, 123
Good: thirty, six, one hundred twenty-three
Unless they are dates or addresses: Blair was born in 1969. He lives at 852 Prospect.