“Good writing is not a natural gift. You have to learn to write well. Here are 10 hints.”
10 Tips on Writing from David Ogilvy
In this post you will find a recommendation for the book, 
Writing That Works; How to Communicate Effectively In Business by Kenneth Roman and Joel Raphaelson.
To this I would add: Stein on Writing and How to Grow a Novel by Sol Stein. And the superb The Elements of Style by Strunk Jr. and E.B. White.
For technical writers, I like, Technical Writing by Diana C. Reap.
