I write a lot before I sit down and put my fingers to the keyboard.
Well, if we define writing as encompassing all tasks necessary to completing a story.
I call it prewriting, where I sit or walk or stand and play through a prospective scene in my mind, once or over and over, working out major and minor details before actually penning a word. I don't always do this, but I find when I do I tend to write scenes faster and they read better-- perhaps because they've been mentallly carried through already. Just like a revised scene usually goes smoother than a rough draft. I feel like I'm just revising a scene I've already prewritten.
A good time to do prewriting is before you fall asleep. Nothing's rushing you or trying to hold your attention. I would not reccomend prewriting during a math lecture-- you might miss something you need on the test. (Yeah...)
Anyone have any other forms of prewriting?