I finally read the whole thing yesterday. This is, without a doubt, the best book about writing I've ever read. It is as important as it is brief. I would try to summarize it, but their isn't any nonessential material. Buy the book, or read some of the rules online (linked above), and live by it.
(I am working on a summary of How to Read a Book by Mortimer J. Adler, and that should be done within a few days. Check back soon.)