Footwork drills accomplishes two things: 1) increases strength and stamina 2) improves your rhythm. A boxer with a good footwork will be able to avoid trouble with his feet and cut off the ring while chasing down an opponent. Solid footwork also means having the stamina to go several rounds without tiring. Boxing is a grueling sport and you have to be prepared to go the distance if your opponent does not fold. The following video demonstrates four different basic footwork drills you could add to your training regimen. Keep in mind that each drill could be used for each minute of a round or one drill per round. It's really up to you. However, do not cheat yourself and avoid these. These drills are very beneficial.
For the boxer's rhythm, you should be on the balls of your feet, moving in a forward and back motion. Do not hop up and down.
For the pendulum, your upper body should remain stationary while your legs move from side to side.
For the step over, there should be two beats: the outer foot lands, then the inner foot.
For the Ali shuffle, again, get on the balls of your feet. One leg goes forward, the other back. Then reverse.