Some things we've learned from past NaNos:
From me: It's okay to leave scenes unfinished. The linear one-thing-at-a-time part of me is rankled but it needs to shut up so I can write. If a scene isn't working, it's okay to move onto another. Sometimes later scenes can help finish out a previous scene. But it's okay if you don't go back right now. NaNoWriMo doesn't mean it's a complete first draft. Some people don't even finish their books. The goal is just 50,000 words.
It's okay to call characters and places xxx. ;-) I never had to resort to that before but I have several characters who get mentioned and might play bigger roles but I don't know enough about them yet to give them good names. So for now they're xxx.
I like discovering things about my characters. I've found myself saying "I didn't know you had a sister who worshipped you. I didn't know you had a talent for cooking. I didn't know you burned out your own magical powers to destroy them."
From Kat: "Drop frogs and zombies with pink ray guns on people." (Which more generally can be translated into let wild things happen and see what happens :-)
Making up quirks can create more problems for the characters --- which takes more words to take care of. For instance I had two characters walking through the woods so I gave one a really bad sense of direction.
Eating and food are great padding.
Anyone else have NaNo tips from previous attempts?