@monus783
I have only two real pieces of advice:
First: Whatever you want to write start writing it goddamn now. I’m serious. I don’t care how bad you think it is, or how little of an idea you have of what you’re doing, start writing. Even if its just the scene you want with no other context added, start writing it.
The only way to get good at something is practice, practice and then practice some more. Try to get at least 1,000 words written a day.
Second: When you aren’t writing, read. Read all the books, and then rip them off shamelessly in your practice writing. This teaches you structure and grammar better than any guide.
It can be anything you want as well, books, fanfics, even just writing out a tv show as if it were a novel.
There is no magic recipe for writing, there is only thankless toil for hours and days that you undertake for the chance of having your words mean something to another human. You will make absolute crap, but do not let that discourage you. Every writer produces crap from time to time, and it is nothing to be ashamed of.