What sort of speed are u talking about cos no1 has even asked yet. are you talking about the speed of 1 particular attack, overall speed, or reaction speed?
you can increase your speed of a particular movement by not only practicing it, but by practising the motion before and after it aswell.
Your speed will improve when your body learns to flow into the motions you want it to, and doesnt have to wait around for your brain to tell it what to do.
Weight training is also important, Not just for getting stronger, but so that you are farmiliar with pulling and pushing heavy weights.