Oh God, I'm a details whore. I keep details on everything in a story, so I know who is doing what and who's related to who and how they're related and how science/magic/Magitek/whatever works in the world/dimension/universe. I keep tons of detailed notes for characters and other stuff in the world for a story I'm writing, if it's going to be chaptered.

If it's a oneshot deal, though, generally I don't keep notes on it as it's supposed to be self-supporting. I don't write many oneshots that aren't original fiction, but they do get written.

I get bogged down in details easily. However, they tend to get written in a story-like format. Even in fanfiction that takes place in established universes, I have to make stuff up to explain changes and plot holes and additions.

I'm an inbetweener, I think, but I also write many stories simultaneously in the same universe. This is useful, because I tend to have a good working idea of things from the perspective of one set of characters and it makes writing another set far easier because I don't have to sit there worrying about details because I know them, and they slip themselves into my writing.

With that said, I used to always write organically, as such, and let the details come out in the writing. I can't do that anymore, possibly due to a lack of time; when I was in school, I rarely paid attention in class and was always turning over stories in my head all day. I can't do that at work, I'd probably kill someone. So, with that said, I find myself keeping a lot of notes and drawing maps and character illustrations. With that said, don't get caught up in the details -- you're likely to find that something you write ends up contradicting it anyway. Things will evolve quite naturally on their own, and you're best to let them!

Another thing I find really useful is writing short stories or drabbles that have little or nothing to do with the story itself -- or making "DVD extras," so to speak. By that I mean, take the characters and put them in an everyday situation and see what they do. Say, like the equivalent of going shopping at the mall in their world, or to a basketball game, or Easter, or something. It will tell you a lot about the characters themselves, but also about the internal and external workings of their environment and culture. These scenes and snippets may never work themselves into the final story, but their influence will.

Clarice wrote:

Another thing I find really useful is writing short stories or drabbles that have little or nothing to do with the story itself -- or making "DVD extras," so to speak. By that I mean, take the characters and put them in an everyday situation and see what they do. Say, like the equivalent of going shopping at the mall in their world, or to a basketball game, or Easter, or something. It will tell you a lot about the characters themselves, but also about the internal and external workings of their environment and culture. These scenes and snippets may never work themselves into the final story, but their influence will.

oh, i'm with you there; it's a way to get to know your characters that's, like, FUN; let them show rather than tell. 
...i use too many semicolons.
thank you all for your input!  i'd like to read your stories some time.

For really short stuff (less than fifteen pages) I usually just wing it.  A few basic ideas, maybe a specific scene, but no great prep.

Longer than fifteen pages, and especially if its screenplay/stageplay and not prose, I do very light character breakdowns and a skeleton of the plot.  For work-for-hire material, I do it real tight, because it tends to make other people more comfortable and sometimes they won't go forward without, including several drafts of synopses and at least one go at the big board where you do an index card for each transitional moment and then cut out anything that isn't fulfilling its very own specific and individual function, before I even start the actual writing.

New ideas, fresh material, are always generated during the writing, though.  Sometimes it's just two characters rubbing against each other just the right way, or minor elements adding up to something totally obvious but that I'd never intended and so I have to run with it.  Sometimes it's just thematic.  Sometimes the family-friendly small 'splodey Summer feel good piece is actually a steamy lovestory of desperation and release on a beach at three in the morning somewhere tropical.  The comedy of manners is actually a tragedy about trust.

I have never understood the need to block out every tiny element including everyone's eye color, shampoo brand, and what they wished for on their birthday candles at seven.  And I find that people who overuse that method tend to also frontload their fiction by placing all that information as quickly as they can in large blocks, forgetting that the thing is supposed to move.

Anyhow, a request: more semicolons, people!  Along with the exclamation mark and the colon, the semicolon is dangerously and boringly underused today!