NaNoWriMo, as you no doubt already know, has all kinds of "rules" about how far into a work you can be before it's "cheating" to use it as your NaNoWriMo project. Fair enough. The idea is not to end the month of November with something super-polished (ha, ha), but to get some words-- a LOT of words!-- on the page.
The official NaNoWriMo organization website says that the only things you're allowed to have done before beginning your novel on November 1 are outlines, character sketches, and research. All well and good.
But here's the thing: I know a lot of you don't work from outlines, maybe CAN'T work from outlines. I know because I've seen the look on your face when I ask you to write an outline or a synopsis. Even when you've already written the manuscript, outlining the plot feels incredibly daunting and unpleasant.
I had the privilege of attending a terrific breakfast panel at the RWA Nationals convention in New York back in late June. The speakers were Steve Berry, Diana Gabaldon, and Tess Gerritsen: incredibly successful, incredibly prolific writers all. And guess what: none of them really write from outlines. Diana Gabaldon, I seem to recall, doesn't use them at all. (She is just as funny as you think she's going to be, by the way.) Tess Gerritsen, who seems extremely organized and "together," doesn't use them either. She wrote an interesting post about her process here, if you want to take a look. But it was Steve Berry's remarks about using outlines that really stuck with me: he said he's used outlines in the past, and it's an effective way of making sure you've got your structure in place from the first draft, but it really sucks all the joy out of the writing. Working on the book became a task to be dreaded, rather than something to look forward to.
This is the opposite of the way I'd always figured I would try to write a novel myself (which might serve in part to explain why I've never actually "gotten around to" it)-- but for all three writers, surprising themselves with what comes next is an important part of the writing process.
Maybe this all comes down to a question of what you're more scared of: a creativity-squelching outline or the ominous and terrifying blank page.
But basically, either way you go about putting your manuscript together, you have my blessing.
Here's a little pre-NaNo reading for you, though, so (regardless of your stance on outlining) you can be mindful of some key points in creating a successful and satisfying novel. I expect you're already familiar with Cheryl Klein of Arthur A. Levine Books; here's a talk she wrote a few years ago called "A Few Things Writers Can Learn from Harry Potter."