Every writer has a favorite book or author to help them in their quest to be a better writer. For myself, it is Mitchell Ivers' Random House Guide to Good Writing which has inspired me to write and to write well.
Ivers' book identifies what is good writing, the voice and tone of writing, structure and plot, grammar, and more. What I like about the book is that Ivers writes in a style that is easy to follow and not overflowing with verbosity: Ivers goes straight to the point when giving examples. So, when you read "Guide to Good Writing" you come away wanting to write not having to write. In other words, what some instructors make to be a chore, Ivers clearly replaces with the joy of writing.
Ivers' writing exercises are particularly useful to help writers develop their own style. The Random House Style manual is included as an appendix to the book. In addition, Ivers includes examples from Poe and Emerson, two of my favorite classical authors. Reread Poe's "Masque of the Red Death" and you will be inspired, if not a little bit frightened!