1) Celebrate! Yes, even you, who started your project but didn't finish. The last thing you should do is toss it aside because you didn't "win." Celebrate what you have created (out of nothing!). Recognize it's awesome. Those of you who won should be celebrating too, for creating something out of nothing, and for completing a goal within the time frame. Don't just celebrate sit there and yell "Yay me!" either, go out and celebrate for real in your favorite way. Go out for dinner. Eat some cake. Seriously, acknowledge this. Congratulations to you!
2) Don't let it die. Now that you've partied it up for your story, that should help remind you this is important to you. Sure, you could leave it alone from now on. You could spend an entire month working on a novel to get nothing in return but the ability to say you wrote a novel. But I think you want more than that...
3) Finish it for real. Reaching a certain word count doesn't mean the book is finished. So, before you begin technical editing, ask yourself, is your book really finished? Are all your characters developed? Do you have abandoned plot lines? Are your transitions smooth? Are you satisfied with the ending?
4) Technical editing. Check out this post for help with self editing, and this post if your wondering if you need an editor.
5) Figure out the best way to stay motivated. What helped you during NaNoWriMo? The support? The deadline? The short time frame? You might not be able to find all those things in one place anymore, but you can still find all of them. Look for writing groups in your community, and if you can't find a live one, you can certainly find one online. Set a deadline for yourself, and enforce it--tell your friends or your writing group so they can help you enforce it. Perhaps another month away is a good time frame, because too little time is too much pressure, and too much time won't get you moving. Figure out what works for you, and stick to it!