All The Tropes:Tips on Grammar

This is a collection of tips on how to avoid making the most common grammar/spelling mistakes when editing here.

Your contribution is more important to us than some minor spelling blunder. If you really don't feel like a grammar lesson right now, just click the back button and pretend this never happened. If you're looking to save our resident Grammar Nazis some grief, however, you may want to read the following.

Capitalization: the first letter of every new sentence should be a capital letter. A new sentence starts after a ., a ? or an !. You already know this, but just in case you don't, you can make a capital letter by holding down the "shift" key (on a standard keyboard it's left of the z) while typing the letter. You should also capitalize people's names (Alice, Bob), movie/book/series titles (Seinfeld, Nineteen Eighty-Four), places which are likely to show up in the Atlas (the Middle East, Paris) and the word I... Although you really shouldn't be using that to begin with.

Punctuation: (? ! , . : ; ...)
- After each punctuation mark there should be a space.
  - Exception: There should be a space before an open parenthesis ("("), not after.
- We cannot hope to instruct you on when it is appropriate to use a comma. The official rules for this were obviously determined by a bunch of drunk guys playing homebrew Wheel of Fortune. Just imagine yourself saying the sentence out loud, pause considerably with each comma, add/remove commas accordingly whenever the pacing seems off and hope for the best.
- ! and ... carry a lot of emotional punch, so use them sparingly. Spamming the ! is reserved for scenes of utmost urgency; spamming the ... is reserved for fleeting streams of consciousness. Neither of these is likely to belong here.

Warning - incoming Wall of Text. Don't despair! You can do it!

This little thing here → ' (the apostrophe) causes a lot of trouble. Probably most of the trouble. Some tips on its use:

One burrito, many burritos- not burrito's. If the s was just added to make a plural, don't use an '.
A lot of words are actually two words crammed into one, with letters lost on the way: do not → don't, they have → they've, we are → we're, it is → it's, and many others (Gotta Catch 'em All!). The ' in this case means "some letters used to be here". If you can recognize a word as one of these, an ' should go where the missing letters used to be.
Julia's eyes, Joe's burrito. When a Y belongs to X, you can say it is X's Y, with an '.

EXCEPTION: pronouns (I, you, he, she, we, they, who, it). These guys are allergic to this use of 's, so they behave completely differently. Most of them even have two different words for "X's Y" and "The Y is X's", just to be confusing.

I → my burrito, the burrito is mine
You → your burrito, the burrito is yours (you're means you are. Your's is not a word.)
He → his burrito, the burrito is his (he's means he is or he has)
She → her burrito, the burrito is hers
We → our burrito, the burrito is ours (our's is not a word)
They → their burrito, the burrito is theirs (they're means they are. Their's is not a word. There usually means a place.)
Who → whose burrito is it? Again I ask - the burrito is whose? (Who's means who is or who has)
It → its burrito, the burrito is its. (This one is a very common pitfall, because its and it's sound exactly the same. As long as you remember that it's is always short for it is or it has, you'll be fine.)

There do exist circumstances where pronouns can legitimately end up next to apostrophes:

Contracted verbs - "Your hat's lilac. Mine's magenta. See the difference?"
The pronoun is part of a relative clause - "Mary bought all that cat John gave her's siblings, she liked it so much," or even "No child of ours's house will ever have mice."

However, the first is pretty much restricted to dialogue, and the second, while technically grammatical, is clunky so is best used only when there's absolutely no alternative. For general prose, avoid both.

When in doubt, leave the apostrophe out.

Some tropers confuse "would have" for "would of", probably because of the similarity in pronunciation. You can say: I would have said it better, but not I would of said it better. In the same vein, don't say "alot". It isn't a word. Just remember that "a lot" is the opposite of "a few", and the "a" isn't part of the word "lot". There is a word "allot", but it has nothing to do with "a lot".

For more sesquipedalian details on this, see Wanton Cruelty to the Common Comma, The Big List of Booboos and Blunders.