Write what you feel most passionate about. The type of books that have stayed with you the longest, that have really shaped who you are as a person, that have given you dreams and nightmares--those are things worth writing about.
For me, I love reading fantasy fiction, and elements of fantasy will certainly be present in almost all my work. I like science fiction, but usually only love it when it starts to border on fantasy (when it doesn't work to adhere to stringent scientific rules or plausibility). No one can read my stories without seeing my love for fantasy.
The stories I have enjoyed most in my life have been Robert E. Howard's Conan stories. These are grossly underestimated. Bob Howard was a brilliant man, and his intelligence shines through in these stories in his passion for ancient times, the folly of civilization, and the evil of religion. Whether or not you agree with his anti-theist themes, they are ever-present and powerful.
I've probably read A Spell for Chameleon by Piers Anthony twelve times. That's the first book that got me into reading.
But what's the first book that changed my life? A Catcher in the Rye. I read it very young, and it made the whole world make sense. Holden Caulfield made me feel like I wasn't alone, and that other people too saw the way society changes people too easily, how shallowness is lofted as a virtue, and how too many people choose not to notice the problems of the world around them. I am certain that if Holden had been at my school, we would have been friends, and would have listened to Nirvana together. He would have been just as big a fan as I. Things like Nirvana, and A Catcher in the Rye, proved to me that art could really change people, and criticize the world in intelligent ways. That's what made me want to be an artist.
The books that have impacted upon me the most are the aforementioned, 1984, All Quiet on the Western Front, Lord of the Flies, Heart of Darkness, Fight Club, Fahrenheit 451, Brave New World, Of Mice and Men, a small selection of Conan stories, and A Clockwork Orange. It's a short list. Those aren't the only books I love (indeed, my favourite genre only crops up once) but they're the ones I truly wish I'd written. And what could inspire my work more than that?
I was also very inspired by two poems in particular: Always Comes Evening by Robert E. Howard, and The Phoenix and the Turtle by William Shakespeare.
If you're a writer, you'll probably have a list like this. It doesn't matter what's on the list, and if it is populated by the genre you enjoy reading the most, then that's great. If anything, you'll probably have an easier time finding story ideas. Nothing wrong with that. All I'm suggesting here is a different way of deciding what you should write about. It's not what you love, it's a question of who you are, and the answer to that rests with what has impacted upon you the most. The goal of narrative, after all, is to impact upon others.
Now, one needs pictures to stick things on Pinterest, so this one represents something that to me both hurts and feels good. There's beauty to me in the idea of nature growing over the remnants of high civilization, but there's also sadness and horror in it. So this one's for Pinterest, and I guess for me:
(I must note that I in no way believe this sort of writing, this desire to change things, is any better than writing for enjoyment. It is merely a question of knowing who you are and being honest with yourself. If what you love are fun stories, for instance, if that's what made you want to be a writer, you'll probably be really good at writing fun stories, and the world needs fun stories just as much as it needs sombre, gritty things. What I love are dark, gritty stories. That's the only reason I want to write them. It is not because I think my goals are any more important or worthwhile. I have to say this because too many authors use words like "serious fiction", and draw a distinction between "literary" and "popular". Such distinctions disgust me, and I have to make it perfectly clear that I am not one of these pretentious douche-bags.)