Imagine being able to go into a bookstore and choose which shelves your book will be featured on. When you write and publish an eBook, that's exactly what you can do. All the book selling sites separate books by category, just like physical bookstores put books on shelves. The advantage eBook writers have is that they can make their book appear on multiple shelves at the same time. Your book can be featured on the romance shelves, mystery spots, short story sections, and humor shelves, all at the same time. This means more eyes on your book, which means your sales will rise. It's book marketing without actually having to do any selling. 
Getting in Categories
When you publish a book online, you're allowed a certain number of book category choices, depending on where you want to offer your book. Every site has its own finite list, though. If you want your book to appear on more that the designated number, you'll have to get creative. Amazon, iTunes, and other book sales sites categorize your book not only from the sections you chose, but also from the keywords and description in your book listing. The easiest way to take advantage of this fact is to use the right keywords.
Keyword Strings
Just like categories, online sites allow a certain number of keywords on each listing. They all consider all the words and spaces between commas as one keyword. So, brown shaggy dog, purple dog leash, train your dog to take walks counts as exactly the same number of keywords as dog, leash, walk. Keyword strings are smarter ways to use that valuable keyword real estate. The secret is to finding the right keyword strings to make your book end up on the right virtual bookshelves. Luckily, Amazon has kindly published a listing of keyword phrases that guarantee listing in its categories, as long as you list them between two commas. It's a simple page called Selecting Browsing Categories, and it contains links to pages for categorizing the major book niches such as romance and Western.
Submitting Your Book
No matter where you publish your book, these keyword phrases will work for you toward getting your book onto the right virtual shelves. Of course, you don't want to fill your keyword space only with these keyword phrases. Readers use the search engine as well as perusing category pages. Aim for three or four good category phrases and fill out the rest with good search phrases people would use when looking for a book like yours: train dog for walks, or modern Western romance. Using both types of keywords will guarantee the maximum number of people will have eyes on your book when they look for something to read.
Keep The Faith and May the Force be with You!
