Rewrite! No one ever writes anything well the first time. The first draft cannot be the last draft. (I rewrite my work fifty-sixty times—or more). Here’s a tip: read your first draft, and if you think it’s good, you are in trouble. But, if you read it and you see it’s not that good, you are in great shape—to get going. The more you rewrite the better your writing will be.
Write for readers. Maybe you understand what you have written, but the writer’s job is to have the reader understand it. Keep in mind: writers don’t write writing, they write reading.
Listen. Read your work out loud (pencil in hand) and it will let you hear your own writing. It will almost improve itself.