You should write a LOT more than you publish. Even Tolkien had a Slush Pile, which is a bunch of writings that he had no intention of ever publishing, or that he deemed so bad that the public would never see it. (Part of what makes Tolkien crazy in the eyes of us mortals is that his slush pile is widely considered publishable, among other things.)
What I'm trying to say here, in more poetic terms than I'm worth, is KEEP EVERYTHING. You can always go back to it later, and rehash and adapt. Also don't be afraid of inspiration. I'm trying to write a light-hearted fantasy adventure with a dash of trans for NaNoWriMo, and my inspiration for it? A goddamn rhythm game, I do not cap.
Also NaNoWriMo is an excellent time to give yourself an excuse to SIT AT YOUR WRITING INSTRUMENT AND WRITE. :)