I just finished reading a great book today by Robert K. Cooper called The Other 90%: How To Unlock Your Vast Untapped Potential For Leadership and Life. In the book, he talks about four keystones: Trust, Energy, Farsightedness, and Nerve. Cooper takes you through all four and shows you how to use them to improve your life and be a better leader.
Some of what I read in this book, I had heard elsewhere before, but I liked Cooper's way of relating it to his own life, and in particular his relationship with his grandfather. I found the keystone on energy to be most helpful for me right now. It helped me to see some things that I could do better and showed me how to do that. In just the couple of days that I've been working with this book, I have found what he said to be very helpful.
I would recommend this book to anyone wishing to improve themselves.