It depends on the story. I always keep a small notebook with me, so I'm always ready, no matter where inspiration strikes. Sometimes a title just hits me out of the blue. I'll run with it; my muse helps me come up with a plot, then characters emerge and are fleshed out. More often than not, the idea evolves into the plot strikes first, then the characters and last but not least, the title.
I know writers that swear by outlines and story notes. I'd always shunned them in the past, until I wrote my first novella, currently being reviewed by a publisher. I prefer notes and for my novella I wound up with seven pages worth, a bit of stream of consciousness.
Fellow writers: Which comes first when you're writing?