Simon Winchester read from his new book at Seattle's Central Library last Wednesday night, and as part of his talk he discussed the three needed elements for a successful non-fiction book.
First of all, he said there has to be a good idea. As a newly naturalized citizen of the United States, he sorted through several ideas until he struck "on the word 'united' in the United States." How did that come to be? How had it managed to last?
You might think the next necessity would be decent writing. He said no, the next important thing is structure, some way of organizing the book that makes sense to the reader.
Once again he sorted through several ways of structuring the book -- chronological, by important people in American history, etc. -- until a relative reminded him of the Chinese system of elements: wood, earth, water, fire and metal (there's a sixth -- air). That seemed to him to be a way to put the book in order, although he worried that following a Chinese system might be off-putting to American readers. In my review of the book for The Seattle Times, I did not mention this organizational structure. I thought it a bit strange, but not off-putting. Had he followed it more strictly, or mentioned it more often, I might have found it intrusive. But it stays in the background, guiding the development of the book but not getting in the way.
Last necessity? That would be decent writing, of course. You'll find lots of that in the book.