What is the most successful thing you have done to boost book sales?
As a long-term writer, I would have to say that the most successful thing I've done to boost book sales was to make one of my books perma-free.
The Wife of a Lesser Man, the first in a police procedural trilogy, has been permanently free since 2014, and has been reigning in consistent downloads, averaging about 350 per month, since then. Ranking has changed in time, of course, since many more books in that genre have been made perma-free, but the downloads are still as strong as ever.
Downloads have turned into sales of the other two in the trilogy pretty consistently, too. Some months are stronger than others, like December, which was one of the best months of organic sales I've ever had. But all things considered, readers seem to be checking out my back list in the back matter of that book, and have gone on to purchase my other books.
If you don't know how to make a book permanently free, read on.
Books can be made permanently free on most platforms, simply by changing the sale price to zero. Unfortunately, on Amazon, you are only permitted to put your selling price as low as $0.99.So, it takes a little canoodling to do this...
If you set your selling price to zero on all other platforms (Kobo, Nook, Smashwords, Google Play), Amazon does price matching. So tell your friends or family members (or some author friends) to report the lower selling price to Amazon via the 'would you like to tell us about a lower price?' link at the bottom of the book's page, where the product details are, Amazon will allow the customer to purchase the book at zero cost. If that happens often enough, not sure of the time it takes (some of my books have been permanently free on all other platforms since 2017), Amazon will make it permanently free.