A great reference, if you haven't already stumbled upon it: "The Elements of Style" by William Strunk Jr. & E.B. White. I love it because it's really short but compact and FULL of useful information that every writer should read and keep close to their desk for reference.
Check out the main sections of the book: Elementary Rules of Usage, Elementary Principles of Composition, A Few Matters of Form, Words and Expressions Commonly Misused, and An Approach to Style (With a List of Reminders)...all in a short 95 pages including the glossary.
I've got my copy on my desk next to the Thesaurus and Dictionary for easy access.