Not all books are easy to categorize, especially when they’re a cross-over that blends two or more genres. This will make it even more difficult to find your target audience. This is where you have look closely at your prominent theme. Is it romance? A mystery? Thriller? Horror? Next look at your setting. Is it contemporary? Historical? Futuristic? Dystopian? Use appropriate keywords such as these to help drive the right people to your story.