Best-selling author Thomas E. Ricks has an interesting recent essay in The Altantic, "The Book He wasn't Supposed to Write," about the revision process he went through with his editor, Scott Moyers, as he worked on his newest book.
I'm not sure that all of his advice is readily transferable across contexts, but near the end he quotes Moyers as telling him about the importance of revision: "The first draft is for the writer. The second draft is for the editor. The last draft is for the reader."
You might not always have a second draft for an editor as you write, but it is really useful to keep in mind that there are usually different purposes and audiences for different stages of the drafting process. You write the first draft to discover for yourself what you have to say about an issue. Once you have a clear sense of your own ideas and argument, the best writing will entail a process of revision focused on fundamentally reimagining the writing to make those ideas legible to readers.