I have found that I do so much better at NaNoWriMo when I have a basic idea and outline ready to go. Nothing huge or in-depth, but just a bare bones sketch of what I want to write about.
I was googling for ideas and found this great blog post about outlining. If you need some ideas, or just a kick in the pants, go take a look:
P.S. NaNo starts in 12 days!
P.P.S. Are you doing NaNo this year? If so, let us know how to find you so we can all be friends.