Creating a book can be slow work for some of us. A few hundred words a day will make a book in a year even if you take the weekends off. You need to rewrite, though, so upping your output to allow for revisions might erase your frustrations.
Journalists practice habits that can serve any author. After all, journalism is called literature in a hurry. Roy Peter Clark is a master teacher and the author of six books on writing. He's devised a list of things to get your pen and keys moving faster, many of which work for both fiction and nonfiction.
He borrows from Strunk and White, the style experts. They say, keep it short; erect a pup tent, not a cathedral. You make the writing into something holier on your rewrite.
Lower your standards for your first draft. Clark says, "Let your hands do the thinking. You can raise your standards during revision.""
Shoot for a draft and a half on some portion of the book: scene, chapter, passage. "A blast of writing, followed by a quick read that corrects mistakes and cuts needless words."
Writing slowly is not a burden to bear. "To be a good writer, you have to learn to write slow," Clark says in his blog. "Some sentences or passages just take a long time. But slow writing need not be the norm." For nonfiction like journalism "and all public writing, the goal should be fast writing — or at least faster writing."
Clark reminds us of the noble work of doing less than perfect. Jane Caplan, the late wife of the great medical ethicist Arthur Caplan, once told told Clark, “When Arthur cleans the house, it is never really clean, but it is cleaner.”
You may not get to being a fast writer, but you can practice habits to work faster. At the publications where I first earned bylines, we had a deadline of 4 PM, or Wednesday, or May 5. On that day, as one editor said to us, "The deathless prose goes out the door." That door might be the outbox to your beta readers, or the trusted reader you're swapping with. Nothing gets done without a deadline. Erect yours to give you focus and speed.