plyometrics and strength training will help with power, and beyond that, keep on jabbing. you don't have to bring it all the way back. I bring it back about half way. remember, the jab is more of a set-up punch. so the second one not having all that much power isn't the worst thing in the world as long as you follow with the right.

do this. on a heavy bag, jab in a circle. don't worry about anything but circling the bag (to your left if you jab with your left). and jab fast. if done right, the bag should be held in place by the fact that you're circling it and jabbing it.