"Close the door. Write with no one looking over your shoulder. Don't try to figure out what other people want to hear from you; figure out what you have to say. It's the one and only thing you have to offer."
I think this is a quote that many new writers need to hear, and many published authors need to remember. Trying to write a book because you think the topic is hot right now or because you think it will sell will not serve you in the long run. Sure, you might sell a book or two, but you probably won't be enjoying the writing process very much.
You need to write what you need to write. If you love romance, write it. If you love science fiction, write it. If what you need to write is a conglomeration of three or four genres, write it. If you're in this business for the long haul you need to write what you have to say or you'll burn yourself out trying to please too many masters.
Remember, your style and what you want to write will evolve and change as you do. You're not stuck writing any particular genre or style. The only limits you have are the ones you put on yourself.