When I wrote my first nonfiction book ever (and the following 27), my editor gave me deadlines.
The first one was so far out in the future that I still managed to procrastinate for a few months, before I started to write like a madwoman.
But I found that deadlines made me more productive, so now I use them all the time.
Whether I write fiction or nonfiction. Or even emails.
Other than that, something that can help you get your book written is paragraph by paragraph walkthroughs. Almost like “write by numbers”.
You’ll find that here http://malka.biz/abracadabook