During the KDP self-publishing process, you get to assign your book to up to two categories. These categories are hierarchical and match the categories displayed on Amazon allowing readers to click through the hierarchy of categories to find a book of interest. Get in the correct categories and more readers will find your book.
But there’s more to categories than just another way to display lists of books. Categories are used to determine if you’re a best seller. See the image accompanying this post that displays the ranking of an Amazon book for it’s categories and closely related categories. Having lots of nice category ratings on your product page makes your book look good.
Things to notice:
1) Do well in a less popular category and you’ll show up on the first page of the category display.
2) Do well in a category to display good rating numbers on your book product page.
3) Become and Amazon Kindle bestseller by entering the top 100 Kindle books sold and become a category bestseller by entering the top 10.
So, you need to find categorizes that are popular enough for people to care about and possibly display but unpopular enough that you become a category bestseller displaying on page 1 of the category page. Determine the competition for a category by displaying it and viewing existing book ratings. The categories with the least competition are usually the furthest leaves out on the category tree.
Now for a big trick. There are some leaf categories that don’t show up in the list of categories available on KDP. These are new categories that haven’t made it into the master catalog yet. The only way to get listed in such categories, that are typically free of competition, is to send an email to firstname.lastname@example.org asking for an ASIN to be placed in the catagory.
Find these categories by displaying the leaf categories available in KDP and looking for books that are listed in categories even deeper in the hierarchy. For example, consider this category hierarchy:
Kindle Store > Kindle Ebooks > Crafts, Hobbies & Home > Animal Care & Pets > Dogs
In this case, “Dogs” might be one of those special leaf categories (it’s not — I’m having a hard time finding an example).
So, go for the longest categories you can find and keep your eye out for those special categories that can only be entered by special request for great results. Get in the Kindle top 100 or the category top 10 to become a Kindle or category top seller.