I thought Leadership Secrets of the Rogue Warrior by Richard Marcinko (the famous Navy SEAL guy) was a really good read though certainly not very PC.

IMO, leadership is a matter of personal charisma, integrity and competence. Some people tend to be very aggressive, backstabbing their way through the ranks to get promoted and enjoy their moment of fame. Sometimes they prevail over more competent but honest, quiet individuals. However, that does not really make them assertive or successful in the long run because anyone worth their salt will see through them easily. Aggressive self-promotion is simply no substitute for real leadership.

As Marcinko points out better than I ever could, you cannot be a good leader or a confident person (the two are basically the same) unless you believe in yourself and work with 110% intensity to achieve your goals, be it education, career or anything else in life. By doing so you will automatically improve your self-esteem. Truly assertive people (assertive in the good sense) always lead from the front. They inspire others by doing, not saying. That's why all the motivational talk so popular these days will be to little avail unless you back it with real action.