Finding a literary agent has become increasingly difficult. That's why many authors choose to go the self publishing route. When you upload a digital self-published release, you’re allowed to choose several categories/genres for your novel. You need to choose a broad genre that fits your right readers' expectations. Then, you choose a niche, preferably one that isn’t heavily populated, that also fits your novel. For example, if you've written a mystery that involves a detective, you might pick 'Mystery, Thriller and Suspense' category. However, a look at Kindle books will reveal there are107,974 offers...the number of ebooks using that category. Go to a subcategory, say 'police procedurals', and this number drops to 4,844. Explore further. Maybe your detective is a 'cat sleuth'. In that case the number of books drops to a mere 23. You'd be by default in the top 100!  A word of warning: if you DON'T have a cat sleuth, don't choose this, just to get a better ranking. Misleading niche readers will hardly gain you good reviews!