Is it a good idea? Yes, if you get the basics of your novel clear first. According to NaNoWriMo rules, you can begin with an outline, notes, and character sketches. That's vital, because launching in to write a novel in 30 days without a sense of direction can quickly lead you to a dead end.
If you're going for it, I encourage you to make sure you have your basic story equation in place. My previous two blogs have been focusing on these vital story elements: 1) the story catalyst, the event that hooks the reader and signals the first surface problem; 2) the deep-story problem that stems from the protagonist's inner struggle and emotional journey; 3) a fascinating, dimensional, and active protagonist driven to go the distance against the odds. If those elements are working in your novel, the work you do in 30 days or six months will pay off instead of fizzle.