If you can only read ONE book, this is it:
Leapfrogging the Competition; Oren Harari
Other helpful books:
Selling the Invisible; Harry Beckwith
The Invisible Touch; Harry Beckwith
500 Year Delta; Watts Wacker & Jim Taylor
22 Immutable Laws of Marketing; Al Ries & Jack Trout
22 Immutable Laws of Branding; Al Ries & Laura Ries
Fast Company Magazine
Anything by Jeffrey Gitomer