I have tried to do Nanowrimo several time and have failed pretty much every time. Anyways looking back, I made a lot of mistakes and here is my advice.1. Know your character.
The worst writing that I have seen in a book, is underdeveloped characters. Define who they are and make sure to stick to that. I love making charts about them with traits, memories, relationship, appearance and random facts that help you make the story.
2. It doesn't have to be perfect.
Pretty much every author does several drafts of each book and a story can completely change in the time. Don't worry about plot holes or continuance of the plot. You need a full draft before you can properly edit a book.
3. Write when you want to.
Find what works for you and write when you can. Don't worry about your word count till August 31st and don't stress about a low word count. This is a challenge to finish a novel. Try your hardest, but if you fail, there is always November.
4. Have a support system.
Find friends that are doing and have a chat on Google+ or Skype once a week, while it isn't the most productive time, it is a lot of fun. You can still have a personal life, if you work ahead. Just try to make it work and don't stress about it.
5. Don't let shiny new ideas distract you.
Focus on the book you start with and try to finish it. SNIs are evil and hard to ignore. Just write them down in a note book for the future.
Most of all good luck and have fun. Also don't move during Nano and enjoy the extra day. =)