For creative writers
The elements of style - William Strunk, Jr.
Asserting that one must first know the rules in order to break them, this classic reference book is a must-have for any student and conscientious writer.
It gives in brief outline the principal requirements of plain English style and concentrates attention on the rules of usage and principles of composition most commonly violated.
Basic rules of punctuation.
Does exactly what it says on the tin.
Masterclass PDFs (thanks to Dave Pescod)
http://www.tindalstreet.co.uk/submissions/
[Right click and download on the links to save to your PC]