To become bestseller kindle book, there are many ways to achieve it. But, selling kindle book with list building technique is very good tactics. Just upload your book on KDP, but do not enable enroll option, set price to anything you want. Also upload that book to smashword and set price to free download. After that, tell amazon that there is your book in smashword that free to download, ask amazon to set that book for free forever. Inside that book, insert link to your squeze page. Trust me, you will have a massive email list.
Then, with this email, you can send email about your next book.