I've recently taught a workshop about beginnings at a wonderful writing conference, Writers at the Beach: Pure Sea Glass and one of the things I suggested to the participants was to keep a journal of opening lines. So, every day before I write, I come up with a few quick sentences that could start a novel or short story. The joy is that I can go anywhere with this because I don't have to finish the story (though every now and then I come up with something I'm interested in). And there's no revising...just write from the gut.
I also feel that this practice has sharpened my writing and that I'm getting to the point more quickly, especially in the beginning of my chapters and scenes.
I believe I first read about this idea in Writing Down the Bones, the classic writing book.
Here's one of my beginnings; I wouldn't usually write about something like this, but I was having fun: It was the way the wind was so relentless. Every day. No one had seen anything like it, not even the old-timers who said they had seen everything. Roofs were in danger, trees were cracking, and the wild roaring was enough to send anyone over the edge. So the village decided a sacrifice was needed.