The best writers are also voracious readers. Whatever type of writing you want to do, read, read and read some more of that same type.
I went to a writer's convention years ago. One of the writers said to find a book you really like, then type out the first 25 pages of the book word for word. It is supposed to give you the feel of language as used by professional writers. It is also supposed to help you understand punctuation and grammer better.
Of course, you can't use the pages you copy for anything but learning, but it is a good exercise.