I follow a lot of different writers and look at their style and how they use language.
I read a lot. I find that the more I read, the more my writing improves.
Reading allows you to see how language flows and that subsequently, gets carried over into your writing.
You can also study the craft of writing: grammar, spelling, how to develop your ideas and stuff like that, but there's this editor-- the first I'd ever heard, but rather well-known in writing circles-- who some even call legendary-- Alan Rinzler, who suggests something just as easy: keep reading and writing!