It takes two things. No, make that three things:
1: You have to need to write, long and often. You think that skipping meals or sleep because you’re writing is normal.
2: You have to have something to say that other people might want to read.
3: You have to persevere LONG past the point where a sane person would try some other career.
The grammar, style, spelling: Important, but you’ll get them because YOU need them to do what you must.