> "After writing the first draft, try explaining to a friend what you just wrote. Then replace the draft with what you said to your friend."
This is the single best thing you can do to improve your communication skills, whether it be in writing or speaking. You're forced, out of courtesy and respect for your friend, to find the heart of the matter and you make it accessible.
(I'm currently in the middle of a 1,000,000 words stream-of-consciousness writing project, where I write exactly whatever's coming to my mind with as little editing as possible. I'm approaching 500,000 words now. It's pretty enlightening.)