If you're participating in NaNoWriMo on November 1, starting off with nothing -- no characters, no plot, no nothing except a willingness to write -- is certainly possible, and perhaps for you, it will work.
If you'd like a safety net, that is, some idea of WHAT you'll be writing in November, I'll be presenting some "quickstarts" for you over the next couple of months. Primarily, these will be exercises.
Are you breaking the NaNoWriMo rules by doing some exercises first?
Does that mean I can't use an outline or notes? Outlines and plot notes are very much encouraged, and can be started months ahead of the actual novel-writing adventure. Previously written prose, though, is punishable by death.
So you can do all the preliminary exercises you wish -- just don't start the actual writing until it's November 1, 2012 in your time zone.
The first thing you might want to do is to choose your fictional genre. Will your novel be:
* a romance
* a Western
* a mystery
* a thriller
If you have a favorite genre (I love mysteries), then that could be the genre you pick. OTOH, if you feel you could easily write a romance, choose that genre. Knowing the genre you'll be writing in helps you, because it limits your choices, and helps you to structure your novel, even as you're writing it. There's nothing more dispiriting, even in NaNoWriMo, if you feel that you're not developing a story -- that you're just typing. :-)
You could read a few mysteries, romances etc over the next couple of months to help you to decide, if you don't know instantly what genre you'll pick.
October 26, 2012 Update
I wrote this blog post way back in 2006. It's still good advice, but of course you don't have months before NaNoWriMo starts -- you have days.
The advice stands however: pick a genre before November 1.