Here's the age old question that attaches to any challenge when you're first starting out. Thankfully, when it comes to NaNoWriMo this one's easy to answer.
You've got to pump out 50,00 words to win, which means a lot of things. You've got to to just pump out words, meaning you need to be able to work with an environment where the setting, characters, and plot are all familiar. You can't stop every two to three sentences going back and editing because, let's be real, you won't have the time to go back and edit period.
So the most obvious answer to this question, is to seemingly pick a project you've already been working on. Time to add 50,000 words to that concept you've been tweaking on your word processor for the last few months. "Seemingly" is the key word here.
As you're probably already aware, there are generally "two kinds of people" to things. There's no exception here. There are two ways friends of mine utilize the NaNoWriMo challenge. On one end, friends will utilize the month to get further and or complete a project they've already been working on. Reminding themselves along the way, not to edit as they go.
That's the one potential danger in selecting a non-completed project for NaNoWriMo, you'll be tempted to go back to words that aren't part of your 50,000 (and by the way, its cheating to use any words that weren't generated during the challenge). If you can avoid either of those temptations, then definitely utilize the month to complete that project you've been working on!
Here's the other side of what I see friends do with this challenge. Many of my friends start from scratch for NaNoWriMo. Brand new project, new characters, new settings, etc. This is not a challenge I'm particularly brave enough to attempt because I'm the kind of writer who really needs to plan ahead of time. Arguably that is what the month of October is for, but my planning and research phases last much longer than four weeks.
Don't write off this way of handling the NaNoWriMo challenge right away though, because there is one huge advantage to braving a "from scratch project." These writers, in their spontaneity, are training themselves to generate creative content on the fly and word counts as well. I'm definitely not brave enough to try that for myself this year, but some training for the future isn't such a bad idea.
Which brings me to the first and probably most significant piece of advice when it comes to NaNoWriMo, and winning the challenge itself.
It's all about quantity over quality.
Whichever method you plan to utilize this year, don't worry about the tropes you'll be scrapping together or the corny emotion that will sometimes squirt its way into your writing. That's what editing is for, and editing will come later. Not in November, but later. The 50k is your goal. When you turn in your manuscript to the lovely staff at NaNoWriMo.org, they're not going to look at your clumsy grammar or your clichés that need to be chopped up later. They're going look at your word processor's tally of 50,000 words. Nothing else.
So pick a project, stock your pantry/fridge with your "thinking snacks," get your focus music/environments ready to go and get ready to put the petal to the medal November 1st. Oh yeah, and have fun! (I mean that literally, even though this challenge can leave you in a panic when you're desperately writing for an entire thirty days.)
If you haven't registered yet, here's a link to the webpage to do so:
Follow the simple steps, register your novel and prepare for November!