Okay. I have done NaNoWriMo one year (2011) and I'm doing it again this year. I did "win" last year, and I've been pretty happy with what I wrote. I had a lot of re-writes to do, but that is not related to NaNoWriMo. It was my own fault for not checking dates and not having a definitive plan for the witches in my series.
I've seen that a lot of people who do NaNoWriMo are having problems with what they have to work with AFTER NaNoWriMo is over. I've heard that they have "won a mess" of a manuscript and they aren't sure what to do with it.
Here is my advice on NaNoWriMo:
Don't push yourself too hard. If your writing seems to be coming out like crap, pace yourself. You don't have to win. If you happen to hit the 50,000 mark, then that is great! If you don't, then that's okay! At least you have a start. NaNoWriMo is about motivation.
USE the forums! If you get stuck, take it to the forums! While you're there answer question other pepole have posted. One of my favorite things about NaNoWriMo is the support in the forums. NaNoWriMo is about supporting eachother.
Once you have written that 50,000 words, or at least have gotten a start on that total, keep in mind that the approximate length of a novel is 70,000 or more. That means you still have some writing to do once you hit that mark whether it be during or after NaNoWriMo. Don't fret! That's okay! Any number is good and will give you a foundation to work with. NaNoWriMo is about writing.
I'll be letting you know my progress each Monday (I'll be calling it NaNoWriMondays: A Progress Report) this month, and I'll do a wrap up post on the 30th, so make sure you return to see progress and additional advice!
Oh, and my username is lil87blue if you want to become writting buddies!