My iPad has more than 30 Kindle books I've read about how to market books by indie authors, and I've recommended several to authors who asked me for advice. Here is my shortlist of the best books arranged alphabetically by author.
Ricardo Fayet. How to Market a Book: Overperform in a Crowded Market
David Gaughran. Amazon Decoded: A Marketing Guide to the Kindle Store
Tammi L. Labrecque. Newsletter Ninja: How to Become an Author Mailing List Expert
Helen Sedwick: Self-Publisher's Legal Handbook, Second Edition