From the WSJ, a nice reminder from Darin Strauss about beginnings:

“The clearest guidance on this point may come from the Canadian writer Douglas Glover, a master of narrative structure. He compares a story’s protagonist to a boulder perched insecurely on a hilltop and suggests that we imagine a bird coming along to knock the boulder off the hill. That’s a perfect place to begin—the moment of impact, the start of the trouble. The motion of the boulder is the story.”

Strauss goes on to look at Kafka’s famous opening in The Metamorphosis. We don’t need to know who Gregor was and why he might have turned into a cockroach. First sentence: boom, he’s a bug. The reader is in.

I think this is especially important to remember on your first draft. Start out however you can (it’s important just to get words on paper), but keep in mind that the back story might not be as important as you think. Trying to keep this in mind as I power through my latest first draft.