I hate Erotic Fiction.

In theory, it's supposed to be writing that - when all is said and done - turns you on; gives you one hell of a boner.
Too often, however, have I lost boners to poorly written erotic fiction.
Let me set some ground rules for all aspiring porn writers:

Plot. You need it. I'm not asking for a thousand-page novel, I'm just sick of my porn having no structure, with things (and people) popping about helter-skelter like a bad Scooby-Doo cartoon. Before you write, at least get some idea about how things are going to happen - even if your plot is as simple as "two people get together and fuck", you still need to figure out the where's and how's (it is a lot harder than you would think it to be).
Plot Development. For the love of God stop ADDing out on your story. Plan it out. Flesh it out: if you want two characters to be brought together by a plot device (say, an illness), then don't half-ass it (like this idiot did:[link]); put a little effort into how the characters will interact with each other and whatever situations you put them through.
Character Development. Even if your story starts half-way through fore-play, your characters still have thoughts and feelings and - gasp! Personalities, and will copulate accordingly. Thus, it would pay to at least establish what kind of person they are. Does he like Breasts or Ass? Is he into anal? Is she a squirter? Does he cuddle, is he affectionate before, during and/or after the main event? Is she shy? Is she doing it just for him? Is it his first time with another man? Is he out of the closet? You need to think about details like that. Now, generally, the shorter the story - the less character development you have to do. In flash fics, you can get away with less-developed characters. In longer works, that ain't gonna fly.
Grammar and Vocabulary. Here is where even the best of plotlines may crash and burn. Nothing kills a boner faster than horribly confused sentences, contemptable misspellings, and calling a man's asshole your "pussy". The first two are easily fixed: fucking KNOWLEDGE OF THE ENGLISH LANGUAGE. Also, a dictionary.

The third one - Vocabulary - is a tougher problem. Some words that normally should be passed over can (sparingly) be used in certain contexts.
Pussy: only in reference to lady-parts (never manly-bits, or nether-bits), and only if there is gratuitous usage of various four-letter words.
Tits: only if certain other four-letter words are being thrown around - "breasts" are always your best word when referring to her mammaries.
Cunt: Never.
Penis and Balls: Never. If you absolutely must refer to both parts, use words that refer to both parts (genitals, manly-bits, "playset" - ANYTHING but "Penis&Balls"). If you use this term, you deserve to be cock-slapped with a Morning-star.
Dick: where appropriate
Cock: only when the story is racy or "hot'n'heavy".
Testicles: Sometimes. To...anatomical for some settings.
Penis: try to find a better word if you can ("member", "part", "manhood" - it's always best to let the imagination infer, just don't get crazy).
Brown-eye: Go die.
Do you see the pattern?
One should try to stay "generic" when referring to the act or the performer's performers. You don't need to give us a play-by-play, just the high points of what the characters are doing and let our imagination play it out. If you look at good romance novels, you find they don't get (overly) explicit - just enough to get the reader going. It's the same principle that every other genre of literature follows: write only as much as the reader needs to see it. I don't need to constantly know what their hands are doing, I only want to know when their hands do something new.

Do you see what I'm saying?

Anyway, I'll end my rant here - chime in if you have something to add.

Have a nice day!