An old classic, Selling the Invisible by Harry Beckwith! 

The Last Lecture by Randy Pausch. Amongst the life lessons Randy outlines in his book, one stood out to me that can be applied across any situation: When you hit a brick wall, consider another perspective.This is what we do in admissions on a daily basis; whether it's a training program, working a list of inquiries, or meeting with students. When we hit a wall we step back and try a different angle with a renewed sense of motivation. And of course the attitude with which we approach the challenge sets the tone for others to adopt.