Forlorn's got a point. Drafting is a part of the creative process, just as much as editing and everything else. Nevertheless, if you get caught in the trap of constantly going back, you will have to exercise self-restraint.
I tend to work this out with myself by writing my entire plot skeleton from start to finish on paper, and then I arrange the events by writing them again in chronological order of how I want them to unfold, and then I determine how scenes should be presented, and when the outline looks good, I stick to it and write on.
Of course, as you're writing, new ideas may strike you, and it's good to let them in sometimes, but remember that you are the driver of the story, so you have to be the one to wring it in and have it under your control. Character muses may act up and alternate timelines may spring up in your mind, but they're in the backseat. You have no obligation to let them drive.
(F---...am I taking a metaphor from Loren???)