LinkedIn has a section on publishing, and recently members discussed what mistakes kill book sales. We’re going to assume that the book is good, typos eliminated, formatted correctly, etc. Here are some of the mentioned mistakes:
1. Failure to get a content editor who helps deliver the payload.
2. Putting up a cover that leads potential purchasers to misjudge the content. The book just doesn’t look like the kind of book the reader is looking for.
3. A small publisher lacks the capital to give the book what it needs in editing, promotion, sales, etc. A self-publisher fails to understand distribution channels and puts the books into the wrong ones, or into too few.
4. Limited thinking by the marketing team.
5. Spamming instead of promoting.
6. Underestimating the amount of time needed to promote the book.
8. In a print book, choosing a font that is too small. The population is aging.
9. Failing to have friends and relatives, who are interested in your genre, read the book early and post accurate reviews soon after the book is published. Particularly with online sales, someone may mistake the subject of the book, not understand it, fail to see his or her own poor choice, and post a bad review. You need to counter with good initial reviews.
Try everything. Use what works.