How can I get lighter on my feet?

Try narrowing your stance, move your center of gravity some more by doing a jig, like Larry Holmes and Muhammad Ali. Also, if your not contented with your footwork, try wearing heavier boots or lift weights with your legs, it will improve your leg's stamina so you won't be dead in your tracks inside the ring. Skip rope can improve your balance after throwing a punch, because balance is extremely crucial when using a narrow stance, movements must be precise. The jab of Larry Holmes for example, requires him to put more weight on his lead foot and raise his rear foot for more power.