The two biggest things a writer can do to improve is to:
1) Just keep writing. Practice helps a lot here. If you can get feedback, that can help as well.
2) Read as much as you can. Reading helps you learn how the language flows and goes together.
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Don't trash those drafts either. Keep them, put them away for awhile, and then go back and revise or rewrite them. A lot of great literature only became great after multiple rewrites and revisions.
A good book to read would be Stephen King's "On Writing". It has a lot of good advice and it's not a dry, boring read.