When I ponder the question with my too-organized, control-freak right brain, I think that it is better to outline a story before starting to write it. Work out some of the backstory. Build the characters. Figure out a little of the plot. I think I should work all that stuff out before I begin to write the first draft. Sometimes I do that. I have written several novels based on a pretty solid outline -- that changed as the characters emerged, and almost always end differently than I originally envisioned.
But, most of the time, I get an idea for a story or a character and I just sit down and start writing. The first draft meanders around something awful, but I immerse myself in the story world and I get acquainted with the characters as they reveal themselves to me. I gradually tighten up the story line once I know the actual trajectory of the story. Then I go back, add detail and polish the writing in the second through the seventh drafts.
I enjoy editing (did I mention I'm nuts?), but I love rooting around in that first draft, looking for the nuggets of interesting character and potential conflicts! I usually don't do a lot of drafting over the summer. I'm making an exception this year. The working title is Miss Loretta's Pies and Whatnot. Miss Loretta owns a bakery in Sevierville, Tennessee, and she bakes a mean pecan pie. She's also an MIT grad who specializes in computer security. She has some issues with fitting in a small Southern town. It'll be interesting to see where this goes.