Short answer: you don't. At least not if you're me.
Almost three years ago I began writing my first novel, Along Came December, during NaNoWriMo 2013. Since I was on pace with NaNoWriMo's daily targets, not to mention fresh off the turnip truck, I figured I'd be finished the novel by January 2014 and published by summer of 2014.
Then again, ignorance was bliss. Since I was obviously a genius and would get snatched up by a literary agent/editor/publisher/God right away, all I had to do was write the book and the rest would take care of itself. But when summer 2014 rolled around and I'd just barely finished a first draft, I had to readjust my expectations a bit. No problem, I'd be ready to start querying in January of 2015 and then all my dreams would come true.
It wasn't until September 2015 that I'd done as much with the novel as I could, and it wasn't until November that I sent out my first query letter. Which came back with a rejection in less than two hours. True story. And when I'd gotten more than eighty letters with the same (canned) message, I decided I wasn't going to wait for someone to give me permission to tell this story. Hence, self-publishing. Hence, more edits needed on the novel now that there's no hope of an agent/editor in the picture and I'm the only one who can make it better. Hence, back into the rewrite trenches.
Hence, novel number two on hold.
When I'm writing well, I'm all-in obsessed. The story is the first thing on my mind when I wake up and the last thing I'm thinking about when I go to bed. I rewrite in my head while I'm in my car, at the day job, at the grocery store, wherever, and all I want to do is get home and put the new ideas on the page. I'm so immersed in the story that everything else kind of drops off the ol' priority list. Which, of course, can occasionally have real-life consequences, but who cares? I'm writing!
However, it also means that making progress on any writing other than what I'm obsessing over is like trying to drag yourself through wet cement by your teeth. It doesn't work. During NaNo 2014 I started working on what is now Novel #2, but I couldn't write anything that wasn't total garbage. The same thing happened during NaNo 2015, and in the few false starts I've made since. I just can't seem to compartmentalize my writing enough to live in two separate worlds and somehow make both of them come alive for me. It's one or the other, and right now the firstborn gets priority. At least until it leaves the nest and makes room for something new.
Sorry, #2. I promise, I will come back for you. Hopefully in January.