Here is a well-reviewed book on this topic: http://www.amazon.com/Style-Clarity-Chicago-Writing-Publishing/dp/0226899152/ From the editorial reviews: "Telling me to 'Be clear,' " writes Joseph M. Williams in Style: Toward Clarity and Grace, "is like telling me to 'Hit the ball squarely.' I know that. What I don't know is how to do it." If you are ever going to know how to write clearly, it will be after reading Willi…
Then it teaches methods for applying those principles.
So instead of teaching rules, it teaches how writing can be clear. Instead of "don't use passives" it shows when a passive verb makes the writing easier to read. It teaches how much new information to put in a sentence and where to put it. And it shows how to connect this sentence to the next for simple flow.