I find that ideas percolate in the back of my mind for quite a while before they turn into stories. Once an idea takes hold, it usually has a lot of associations around it—themes, characters, plot elements. Still, I won’t sit down to write until the first sentence comes to me. The first sentence can determine the tone of the entire piece, so I never force it. I just trust that it will come—almost always, when I’m not thinking about it—and when it does, I run to the computer to begin.