what is currently trending in YA and MG. The the hilarious Kiersten White posted her idea that will meet all the trends.
My own personal opinion is that writing to trends makes you look every bit as silly and Kiersten did in her post, and a LOT less funny. Trends in this industry come and go so fast and the business moves so slow that timing is really all about luck.
Write what you love, work hard at your craft and eventually the rest will work itself out.
BUT if you happen to be, let's say revising to go on submission for a supernatural psychological thriller right when Mandy Hubbard says something like, "MANY editors would love a thriller/suspense/horror. Most said more of the psychological kind, not the slasher/guy-with-a-chainsaw kind, but there was room for both, really. If you've written something seriously, insanely scary, you're in luck."
Well then, you deserve a cookie.