You win NaNoWriMo by writing to your word-count goal by midnight on November 30.
Every year, there are many, many winners. There are no "Best Novel" or "Quickest-Written Novel" awards given out. All winners will get an official "Winner" web badge and certificate, and bragging rights for the rest of their lives.
- Note: You must complete this step by 11:59 PM (your local time) on November 30 in order to officially win.