All of these are available through Amazon-- and are books you should have on your shelf if you want to be a professional, most should be available at your local library as well-- and I'm providing the ISBNs so you can look them up.
Comics and Sequential Art: Principles and Practices from the Legendary Cartoonist (Will Eisner Instructional Books)
Comics and Sequential Art
by Will Eisner
ISBN 978-0393331264
W. Norton and Company 192 pages

by Scott McCloud
ISBN 978-0060976255
Harper Paperbacks 224 pages

by Scott McCloud
ISBN 978 -0060780944
Harper Paperbacks 272 pages

by Andy Fish
ISBN 978 -0785826705
Chartwell Books 224 pages

Framed Ink: Drawing and Composition for Visual Storytellers

by Marcos Matue-Mestre
ISBN 978- 1933492957
Design Studio Press 128 pages

(This is advanced)