How often do you go back over what you've written, and edit your work? Do you prefer to leave that until much later in a project? Or are you forever going back over your work and changing little things?
If I'm not careful I'll rewrite the same #*@!ing paragraph or two over and over, sometimes resulting in completely scrapping the whole thing as malicious doubt storms the Normandy of my mind, leading to an existential crisis about whether or not I'm wasting my time writing, accompanied with contemplating the point of living, and ultimately falling into depression. Going back and fixing little nit-picks is alright. A missing word, spelling error- small things. Otherwise, it's way easier and more productive (and less depressing) for me if I wait to rewrite until I've completed the draft. You'll have the context of the whole to work with. Easier to see the bigger picture and the potential. You have more information to work with, resulting in better decisions during the re-write process. Not to forget the satisfaction and warm feelings associated with completing a full draft!
I'm dreadfully lazy when it comes to re-writing/editing, I'm afraid... I can produce masses of text in a short amount of time, but can never get myself to edit. Probably my fatal flaw.
I have gone back and re-written a few scenes here and there, but for the most part, I highlight problematic areas and leave them to come back to later. I put a little note in the margins or in parentheses about what I want to fix, then move on. I plan to address all those concerns after finishing the first draft.
I heavily, heavily edit every scene before it goes on the shelf and I move on to another scene. When I'm up to date on my writing quota, I intermittently go back to old scenes and edit them again. I don't actually recommend this for practicality; it works for me because I only take pleasure from my writing when it's at a certain level of polish, and without intermittent doses of pleasure, I won't write. I've been reading Emma Darwin's blog, and she's firmly against the "changing little things", phrased by her as "don't fiddle." I don't know that I actually agree with her for me, but here's her argument: http://emmadarwin.typepad.com/thisitchofwriting/2008/07/fiddling-hangovers-and-the-paris-review.html