I like combinations that you don't see too much of - horror-comedies, romance where you'd normally never see it and less romance where you'd expect a lot. I enjoy writing about angels who hate their lives and demons who have good intentions.
I think you should write something that you would like to see. Something you haven't seen yet that you've always been itching to watch / read.
That's what drove me to start working on a story about mafia prize fighters that offsets the theme of organised crime with the tone of a sports manga. It's stupid but I really think there's a lot of potential in unexplored territory. It might become a comic one day? Who knows.
Hell, Hideo Kojima made himself world famous by throwing together spies, sci-fi, actual magic and... the concept of being a good dad??? even delving into both ridiculous comedy and heart-wrenching drama with equal amounts of creative passion.
Honestly: there are no bad ideas or even boring ideas, just bad or boring execution. So long as you have the drive to make something the best you can you will create something worthwhile. Hell, you could make something that everyone's seen before but take a whole new angle and make something iconic.