I'm currently reading a book called:
Mastering Composition - techniques and principles to dramatically improve your paintings. by Ian Roberts.
Northern Light Books
ISBN-13:
9781581809244
This is a great book for anyone looking to improve their composition skills. I've learned a lot from it so far. There are great exercises in it that are recommenced to do everyday, just like music practice, that help you to understand composition, both as a whole and in shapes and values. The book breaks the mastery of painting into component parts so that you practice in the most effective ways. I highly recommend this book to anyone who thinks (or doesn't think) their composition skills need work (like myself), or for anyone who doesn't understand it's importance in painting. This book is not just for beginners but for seasoned painters as well as Mr Roberts gets into some complicated stuff.