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 Williams' book, which is a rigorous examination of--and lesson in--the elements of fine writing.