That really, really depends on what kind of project. But one thing has been helpful to me pretty much regardless. I make an outline of the Big Steps in the project (move house; have a baby; kick ass in my profession; retire; dire), and then I make an outline of what needs to happen for the first Big Step to happen. (Move house = find house; arrange for moving; pack; move; unpack; settle.) Then break down just the first substep, if necessary, until the broken-down pieces are pretty small.

Other than that, I'd need more details. But I'm also reasonably good at this sort of thing, so ping me if you want to sit down and brainstorm. I *love* organizing.