In addition to writing, you're gonna need to read. A lot. Because writers don't just write. Writers also read.
Fiction. (That's a no-brainer.) Non-fiction. Essays. History. Science. Poetry. Read them all. As much as you can.
And if you're planning to write romance, mystery, science fiction, or any other genre, read them.
For the love of all that's holy, read them.
Read them a lot.
Grab a stack of whatever genre you're gonna write and read them.
Find their classics and read them.
So you learn what makes them tick.
So you don't try to reinvent the genre wheel.
So you know what's been done--and know variations of what's been done.
So you know what your readers are gonna expect from you.
Look--if you decide to write sword and sorcery and you end up with high fantasy, you've got a problem.
If you try for a hard-boiled story and end up writing a cozy, your readers'll be pissed.*
There's another reason you should be reading (fiction, non-fiction, essays, poetry, etc.), but we'll cover that in an upcoming post.
For now, go get you some books and get started reading.
*If you have no clue what "hard-boiled," "cozy," "sword and sorcery," or "high fantasy" means, you're gonna have problems. Look them up. Learn them. Remember them. You need to know this stuff, Dudes and Dudettes.