Great points listed above. I was an assistant coach for 8 years and enjoyed that position very much. Later on I became a head coach and had the chance to have assistants of my own and they were invaluable.

One of the things that I feel is important as an assistant is to become really, really good at a couple of things that are vital to YOUR head coaches program that he can entrust you with completely. It might be rebounding drills, and then watching closely for what has been taught to players as they play in games. I found it helpful to have an assistant that was well versed in something that I could delegate to them. As an assistant you feel good when you've been given a responsiblity and it helps to develop a sense of ownership and pride in the program.

I was blessed to work for a head coach that really made me feel like an integral part of the coaching team who valued my input. That made me want to work all the harder for him to insure success. Good luck and have fun!

I am an assistant coach at the small college level now. I was an assistst for a middle school last year (big jump huh?)
My advice would just be do whatever responsibilities the head coach gives you to be the best of your ability. I am lucky in some ways because the head coach has me lead at least two major drills per practice.

I am also able to work a lot with the players one on one. This is one of my favorite things to do.

I think it is very important to make sure that you buy in to the head coaches philosophy. You wont agree on everything but that is ok.