Listen to your words. Make them sound better. Even if you accurately express your message, if your reader can't easily understand it or stumbles because your words don't sound right, then you've done only part of your job. Weigh brevity vs. clarity. Brevity is good.
Clarity is better.
After you've written your first draft, put it aside for a while. Look at it again as if you've never seen it before. Read it quickly for an overview, as a casual reader might. Take the reader's perspective. When you read through your work again, ask yourself whether you can easily grasp it.