First of all, I'd like to tell you that my Kindle book is a novel (for middle schoolers at that), but this tip has worked for many people that I consult for. First, you should find other books in your niche, or similar genre (in my case the Diary if a Wimpy Kid books) and read them. After that, you should write a thoughtful and thorough review, and at the end, leave a link to your book with a bit of context (e.g. "It was similar to x", or "I recommend x for people who liked this") in your review. (Note: you must use the product link tool). This signals to Amazon's algorithm that your book is similar to the book you're reviewing and it will show up on the Recommended Books or People Who Bought This Also Bought tab. The review must be helpful, and if it is your review will likely rise to the top of the book's page and get even more exposure for your book. (Note: if you are using the same name to review that's on your book, you will need to fully disclose and it may not work as well).
Thanks, and good luck!