So you're going to write a novel this month! (Or you're just starting one, or thinking of starting one.) How should you begin?
Here's what I like to do before I start any novel these days—whether I'm trying to write it in a month or not: find a hero novel. A hero novel is a novel that you're going to go back to when you get stuck. It's your guiding novel light. You'll pick it because it's the kind of prose you want to write in your novel, or because the storyline is similar to yours, or because it has a structure you like (three points of view, or epistolary, or in second person, etc.).
For my novel in progress I've chosen The Vacationers by Emma Straub because 1) it's about a marriage disintegrating, which is something my novel is going to touch on, and 2) I read the first few pages and thought, "This is the tone I'm going for."
Once you pick your Hero Novel—and you may have to try a few out—read the first few chapters slowly, carefully, letting them inspire you. What does the author do that you want to do in your beginning? What does the author do that you don't want to do? Take notes, get ideas for your characters and scenes, for how to structure your beginning...the overall idea is to get excited.
If you want to really get nerdy, you can actually break down exactly what the author is doing on each page. When I was starting my novel When You Read This, my Hero Novel (though I didn't have that term for it yet) was Where'd You Go, Bernadette because it's also told in emails. I actually made a chart of each page of the first 30 pages or so: P1 - Email where X happens; P2 - Email where Y happens. This way I got a sense of her pacing, because I knew her pacing worked.
Finally, picking a hero novel is fun. You get to read. And we all like that. :)
Happy writing—and happy beginning of NaNoWriMo if you're doing it!