From Just Publishing Advice:
Do you know that you can add more Amazon categories to your book?
You can only select two categories when you first publish your book or ebook with Kindle Direct Publishing (KDP).
But these are not Amazon categories. They are BISACS (Book Industry Standards and Communications) headings.
If you want your new book to be much more visible, you can add up to ten new categories to make your book more discoverable by Amazon book buyers.
. . . .
How to add more Amazon categories to your book
You could use category keywords in the past.
But the only way now is to ask Amazon to add your new categories.
Why would you want to do this?
When you list your book in only two BISACS headings, it’s lost in a sea of thousands upon thousands of other books.
There is almost no way your book can climb high enough to rank in the top 100 books.
If you list your book in Fiction, Romance, or Science Fiction, for example, you have no hope.
Even if you refine your selection from the options available, you are still in a pool of thousands of other books.
For instance, Fiction / Romance / Contemporary or Fiction / or Science Fiction / Apocalyptic & Post-Apocalyptic.
But when you look at the Product Details section, do you see your book listed for any best-selling ranks?
You can check out some top-ranking books on Amazon.
You will notice that when a book has these, the categories are generally narrow and are very rarely BISACS headings.
When your book is in smaller and far less competitive categories, you have a much better chance of getting a Best Sellers Rank.
How to check your categories
A book’s categories don’t appear on an Amazon book page unless it ranks.
Only the general category appears at the top of the page, such as Kindle Store›Kindle eBooks›Science Fiction & Fantasy.
There must be at least two, so how can you check?
Luckily, there is a nifty little free Book Category Hunter tool by the NerdyBookGirl.
All you need to do is paste the ASIN or ISBN, and presto! You can see all the categories.
It’s the best way to start the process of improving or adding categories to your book.
If you only see two for your book and ebook, it’s time to do some work.
Let’s look at how you can do this.
Finding new niche categories for free
When you publish a new book with KDP, you can choose seven search keywords and two categories.
Chosen well, these help readers find your book on Amazon.
You can’t use more than seven keywords, but you can add more categories.
There are two ways you can do your research to find additional categories for your book.
One is free, and the other requires specialized software.
The free technique is relatively easy but a little time-consuming.
You will need to check high-ranking books in your genre and look at the ranking categories.
However, Amazon only shows a maximum of three.
Clicking on a category will only give you a list of more books.
You need to copy the ASIN or ISBN of the books and use the Book Category Hunter tool to access the categories.
Then you can see all the categories for the book with the entire category strings.
The book above has twelve Kindle and ten book categories.
That’s too many to list here, but here are a few examples.
Kindle Store > Kindle eBooks > Mystery, Thriller & Suspense > Thrillers > Legal Thrillers
Books > Mystery, Thriller & Suspense > Thrillers & Suspense > Crime Thrillers > Murder Thrillers
Books > Mystery, Thriller & Suspense > Thrillers & Suspense > Spies & Political Thrillers > Assassination Thrillers
You might need to check ten to twenty books or more to find categories that are a good fit for your book.
When you have your list, you can then ask Amazon to add them. I’ll show you how to do it later in this article.
. . . .
The best way to add more Amazon categories
The big drawback with the free method is that you don’t know how competitive or effective your choices will be.
The only way to get an accurate guide is to use Publisher Rocket to access the Amazon database.
Now you can check how many sales you need to rank in the top ten or at number one. You can check for books, ebooks, and audiobooks.
With the software, you can search for less competitive categories to give your book the best chance to rank.
Kindlepreneur has a terrific guide on how to use Publisher Rocket to find better categories for your book.
Link to the rest at Just Publishing Advice
PG notes that he has been using Publisher Rocket for several years and has found it both helpful and time-saving.
PG notes that he has no relationship with the folks who created and maintain Publisher Rocket and mentions it simply because he likes it. The OP caused PG to rethink some of the ways he uses the program in order to improve the visibility of Mrs. PG’s books.