William Dalrymple, author of From the Holy Mountain: A Journey Among the Christians of the Middle East and many books on India, pens a most-helpful essay on how he goes about writing those non-fiction books.
Note that the process, in total, takes him about four years, only the last of which is devoted to writing the text itself. Of course, Dalrymple is doing a little writing (of the unconscious variety) when he’s making his notes, because that’s what we all do: we’re thinking, “How does this statement fit in with the story I want to tell? How do I weave it into my narrative?” But the act of writing the book proper comes later.
Dalrymple writes notes corresponding to every event mentioned in his books (transferred from his note cards to a laptop), and then, when he’s ready, composes his text. Most writers work this way, myself included. In the old days, I’d write directly from the notecards themselves, after thoroughly grouping them into related piles on my bed, table, or desk (it was fun). These days, my notes are in the computer. Dalrymple revises chapter by chapter. Since his notes (the 400-page event log he’s made) has structured the work for him, he knows where he’s going and can afford to revise individual chapters alone until they meet his standards. Fiction writers could work this way if they wanted to. Indeed, contrary to Dalrymple’s assertion that novelists write out a whole draft and then revise, Richard Rhodes, author of The Making of the Atomic Bomb, revises his novels chapter by chapter, as well. Whatever works for you is the way you should work. The most important result of your choices about how to work is your productivity: are you getting the words on the page at a pace comfortable to you? If you are, you’ll know it; if you aren’t, there are ways to adjust your work habits.
Dalrymple is delightfully honest. His advice about no liquor while writing is sound; so is his admonition about allowing no distractions. Read his whole essay, and see if you can spot the typo his editor left in the text.