But having done this stuff for years, I can say that it's a bottomless pit, a real tar baby to get stuck to. Because the search engines and spammers are constantly making things change.
Key points are 1) Having valuable content, and 2) Using phrases in your title and copy which people are normally associating with that type of content, 3) Sharing the love by linking to people who you find have valuable content related to yours.
A caveat: Google has information seekers. Amazon has buyers. What works for Google isn't exactly the same for Amazon. But if you set your book up in the title right, Google will send buyers to Amazon.
And the million sellers don't care a whit about SEO, btw. Check out John Locke and Amanda Hocking ( storify.com/robertworstell/...) for yourself. (Just sayin'...)