Just like many other skills, the more you do, the better you get.
Writing anything is better than writing nothing. It is an iterative process. The readers do not care (and cannot tell) how many iterations you have made, or how crappy the earlier versions were.
Read good papers, and learn their styles.
Look at suggestions (books, articles, online tutorials, etc.) on how to improve writing.
Aside from telepathy and telekinesis, any other form of external communication has inherently narrower bandwidth than your internal brain circuitry.
The challenge is to figure out what you know that others don’t, and effectively communicate these.
(I used to think that teaching is orthogonal to research. Now I realized that both rely on the above, after being a prof.)
What you want to write might not match what you really have written. To detect this discrepancy, flush your brain cache as follows. After having a draft, leave it there until you have forgotten most of it. Then look at it again.
When you have only minor updates between revisions, show your draft to other people for comments. Ask them to be honest and brutal, like reviewers.
