In the beginning, the most difficult thing about writing can be what to write. Most writers tend to write what they love to read and reading exclusively in a certain genre makes them well-versed in that genre. Professional writers are usually more marketable if they stick to writing one genre, because when you are published you develop a following and your readers, for the most part, expect you to write in a certain genre.
Think about it. Stephen King writes horror. Barbara Cartland wrote romance. Patricia Cornwall writes thrillers. They are not all over the map writing romance one year and science fiction the next. That is not to say that at some point you could not break out of your mold and write something entirely different. Think Nora Roberts as her alias JD Robb.
But what do you do if you are interested in a broad spectrum of genres? You consider yourself widely read and yet, you cannot decide what genre you want to write. Maybe you feel like you are out there floating around like an astronaut in space, with no anchor. You may want to write horror but then you are pulled in the direction of women’s fiction and you simply cannot decide. Perhaps it is a fight between memoir and science fiction.
Which leads us back to the pivotal question of what are you going to write? You can do one of two things.
If you are being pulled in opposite directions, you can try writing both initially and from there choose the genre that you write best. Sometimes, you really do not have a clue until you start writing. You may need to experiment and write a lot of different things until you discover what is best suited to you. Yes, it is time consuming, but it is also an effective tool of elimination.
That is not to say you need to totally abandon the other genre. You can also blend genres or have your work contain elements of the genres you like to write. You could write your police procedural with a romantic sub-plot in it. Fantasy with humor. Women’s fiction with mystery.
Whatever you decide in the end, the only way to decide is to keep writing.