While a lot of these are sex and/or slash-related, don't worry: G-rated fiction and on up is certainly welcome on this comm! I think it's just that nothing confuses people more than sex. *grins* Also, it might possibly have something to do with this post being made by yours truly. ;-)
Renegade Slash Militia: Writing and Reference Links
It's exactly what it says, and moreover, includes links to a couple of the sites also listed below. Very comprehensive. There's also links to UK language usage, which isn't so much useful for the GD trio, but Ronnie's from pretty much everywhere, so... ;-D
The Writing Suggestions page, Citizens Against Bad Slash (CABS)
Critiquing vs. flaming: know the difference; Writing tips for the masses; Before you post: a checklist; A glossary of slash terms; and other useful stuff. The Fourteen Rules of Good Fanfic article is particularly good.
Minotaur's Sex Tips for Slash Writers
While everyone probably knows this site, it must be mentioned. A now-static archive of information on gay sex written by a gay man, aimed at the largely het female writers of slash fiction. There is explicit content on this site, including photographs; consider yourselves warned. Not remotely work safe!
Of course! The massive online encyclopedia. Pretty much every kink has at least a wee entry explaining WTF people are talking about.
The dictionary companion to Wikipedia - self-explanatory, I hope.
The Establishment Web site
The Establishment is a role-playing game (RPG) over on Journal Fen; this section of their Web site contains a collection of links to sites with information on the BDSM lifestyle.
How to Write Marginally Readable Fanfiction
By Ms. Nitpicker, a former English teacher. The categories here include sections on dialogue, punctuation, vocabulary, and there's a fanfiction glossary. Plus it's all delivered in a slightly snarky, amusing fashion that makes all that advice pretty easy to swallow. Although, obviously we're just going to ignore her bias against RPF/RPS. ;-) (Recommended by revid.)
Exactly what it says. Not sure how to spell something? Look it up here.
An article from Writer's Digest about how to clean up and clarify your prose.
Dialogue Punctuation Made Simple
This is a seriously kickass explanation of exactly how to use punctuation in relation to dialogue. It is extremely clear and well-written with good examples. Note that it is for American punctuation, but the British does not vary a lot from this usage (the only place where there are differences is in the placement of quotation marks).
Punctuation in Fic
A post with punctuation examples that are specific to Green Day fic.