When you upload your book into KDP, you may choose up to two categories. You can also update your categories by going to your Bookshelf, clicking your book title, then Add Categories in a section called Target Your Book to Customers. When you do this, you are in fact choosing a browsing path for readers, which consists of a hierarchy of sub-categories. Thus, your book is available for readers to discover under each of the parts of that hierarchy. So by carefully choosing your category, and then refining the selection by use of sub-categories, you make it much more likely that a reader will find your book, since the pool of books is smaller with each step down the path.
For example, in the case of my most recent book, Home, here are the browsing-paths I chose:
Look for Similar Items by Category
- Books > Literature & Fiction > Anthologies & Literary Collections > General
- Books > Literature & Fiction > Poetry > Anthologies
- Kindle Store > Kindle eBooks > Fiction > Genre Fiction > Anthologies
- Kindle Store > Kindle eBooks > Fiction > Poetry
The first two (which start with 'Books') come from the paperback publishing, the last two (which start with 'Kindle Store') come from the Kindle publishing.
You should choose a browsing path that ends up with a small number of books at the end of the path. Why? Because then, your book will compete for attention with a smaller pool of books. For example, suppose I would choose a more generic path, such as Kindle Store > Kindle eBooks > Fiction. Then, the book would compete with nearly 560,000 books. By being specific, it competes with 34,000 books in Poetry, or with 12,000 in the category of Poetry > Anthologies.
Some Indie authors take this strategy to a ridiculously narrow level. They figure that they can find a category that has a small pool of books and list it as their books category--even if the book does not really belong there!
I have seen fiction books listed in Health, Fitness and Dieting, in Advice & How-to, in Drama, in Travel.... Even if the pool of books in one of these subcategory is small, it does not serve your book any purpose to be mis-categorized. Your fiction may well be 'dramatic'--but that does not make it 'Drama'. The plot may take place in Rome or Paris, but that does not make it a travel book. One drawback to listing your book in the wrong subcategory is that you risk getting low scores on customer reviews, because a reader expecting 'drama' (as in Shakespeare or Arthur Miller) may not be forgiving when she gets a book that is clearly not drama. Therefore, I advise you to click the subcategory and view the books listed at the top of this list. Then judge for yourself if your book truly belongs there.
I have seen fiction books listed in Health, Fitness and Dieting, in Advice & How-to, in Drama, in Travel.... Even if the pool of books in one of these subcategory is small, it does not serve your book any purpose to be mis-categorized. Your fiction may well be 'dramatic'--but that does not make it 'Drama'. The plot may take place in Rome or Paris, but that does not make it a travel book. One drawback to listing your book in the wrong subcategory is that you risk getting low scores on customer reviews, because a reader expecting 'drama' (as in Shakespeare or Arthur Miller) may not be forgiving when she gets a book that is clearly not drama. Therefore, I advise you to click the subcategory and view the books listed at the top of this list. Then judge for yourself if your book truly belongs there.