If you are a writer, and you have a novel idea that you are excited about writing, write it. Don’t go on message boards and ask random Internet denizens whether or not something is allowed. … Who is the writer here? YOU ARE. Whose book is it? YOUR BOOK. There are no writing police. No one is going to arrest you if you write a teen vampire novel post Twilight. No one is going to send you off to a desert island to live a wretched life of worm eating and regret because your book includes things that could be seen as cliché.
If you have a book that you want to write, just write the damn thing. Don’t worry about selling it; that comes later. Instead, worry about making your book good. Worry about the best way to order your scenes to create maximum tension, worry about if your character’s actions are actually in character; worry about your grammar. DON’T worry about which of your stylistic choices some potential future editor will use to reject you, and for the love of My Little Ponies don’t worry about trends. Trying to catching a trend is like trying to catch a falling knife—dangerous, foolhardy, and often ending in tears, usually yours.
I’m not saying you shouldn’t pay attention to what’s getting published; keeping an eye on what’s going on in your market is part of being a smart and savvy writer. But remember that every book you see hitting the shelves today was sold over a year ago, maybe two. Even if you do hit a trend, there’s no guarantee the world won’t be totally different by the time that book comes out. The only certainty you have is your own enthusiasm and love for your work. …
If your YA urban fantasy features fairies, vampires, and selkies and you decide halfway through that the vampires are over-complicating the plot, that is an appropriate time to ax the bloodsuckers. If you decide to cut them because you’re worried there are too many vampire books out right now, then you are betraying yourself, your dreams, and your art.
If you’re like pretty much every other author in the world, you became a writer because you had stories you wanted to tell. Those are your stories, and no one can tell them better than you can. So write your stories, and then edit your stories until you have something you can be proud of. Write the stories that excite you, stories you can’t wait to share with the world because they’re just so amazing. If you want to write Murder She Wrote in space with anime-style mecha driven by cats, go for it. Nothing is off limits unless you do it badly.
And if you must obsess over something, obsess over stuff like tension and pacing and creating believable characters. You know, the shit that matters. There are no writing police. This is your story, no one else’s. Tell it like you want to.