Do lots of sparring.When sparring do not connect to opponent's face.Train hard and try to develop as much POWER,speed and skill while sparring.When you are in match connect to his face.

This is how you develop more punching power:

do not do bicep weightlifting.bigger biceps contract your punches,making your punches weaker.

You should do PRESS UPS to make your punches more powerful.

You should do PRESS UPS WITH YOUR FISTS clenced to make your punches more powerful.Because more powerful TRICEPS makes your punches more powerful.