Novelist and short story writer Bobbie Ann Mason said in an interview somewhere (on a little scrap of paper torn out of something in a stack of stuff in my office):
"I have always found it difficult to start writing with a definite idea about a character, or even a definite emotion. But if I start with a pond that is being drained because of a diesel fuel leak, and a cow named Hortense, and some blackbirds flying over, and a woman in the distance waving, then I might get somewhere."
I love that because I know exactly what she means. That's one of the most fun stages of writing - when you're right on the precipice of actually putting pen to paper, but that hazy idea is still swirling around and not quite ready to land.