A lot of beginning writers struggle with this question – whether to write for themselves or for their readers. Basically, the answer lies in what the writer wish to accomplish – if it's just for fun and their not concerned with how many people will actually buy the book, then writing for themselves is fine. But, if their goal is to get published and be paid for it, then aiming for a certain audience is a better choice.
Of course, this doesn't mean you should abandon your own style and voice, you should definitely stay true to them. But if you want to build an audience, you need to understand what this audience likes and what interests them. A good way would be to go to the local bookstore and observe people – what kind of books are popular, what people are saying about them, and so on.
You need to ask yourself, who is going to read your book, who is the ideal reader. You can even visualize a certain person, a potential reader, and give them a name, a profession, a place to live. Think about what this reader likes, what are his\her hobbies, passions and so on. Then, when you sit down to write, write for this person. Think about what they would say or how they would react to a certain scene or character. Will they relate to it?
Once you craft this persona, it would be a lot easier to craft your book in a way that will relate to them, so much that they would not only read the book, they won't put it down until it's finished. If you succeed in this, you'll not only get a devoted reader, you'll also grab the attention of an agency or an editor who can see that you know exactly who your audience is.