Also, as obvious as it sounds, make a conscious effort to improve your footwork when you're shadowboxing. Work on "rhythming" a chunk of your weight back and forth from the lead and rear leg, then learn to punch off of that rhythm, throwing your straight punches and uppercut as the weight is pushed forward, and your lead hook/lead uppercut as the weight is ripped back to your rear foot.
Rope drills, like Standard mentioned, work wonders. Assume your fighting stance and weave under the rope. There are many variations on what kind of weave you can work, here. You can drive off of the back leg and advance with it, ideal for closing range. You can weave to your right (under a left hook) and step out with your right foot after pushing off of your left during the weave to set up a sweeeeet right hand counter.
A good drill with the bob/weave is this:
-Throw an advancing 1-2 (push off right foot + step with left foot on jab, drag right foot forward as you throw cross) and immediately weave left (under a right hand), then put a bit of weight on your front foot and then push it back with a pivot to circle off (right hand slides around clockwise to get you into your stance). This little sleight-of-foot gets you in a great position to hit your opponent with something he can't see. Right hands are generally what the doctor ordered, but a lead hand hook or stiff jab will be even further outside his peripheral vision, even if he's in mid-turn to face you. Repeat ad nauseum, and work weaving right (under a left hand), still using that outside step to set up that previously mentioned 2 counter. Alternate between one and the other for the round. The amount of foot placement and proper weight distribution you need to pull it off effectively is incredible, so get practicing!!
Jump-rope really does help, for coordination but I think more importantly for getting you up on the balls of your feet.
