The first thing you want to do is build up your body with bodyweight exercises, pushups, pullups, and most importantly body squats, all power pinchers have built legs, that way you can gain strength but maintain agility, I would stay away form weights they take away from functionality.

Next, get as heavy bag as you can hit, all power punchers have been known to hit really heavy bags, including iron mike

And third, throw your punches with power, throw as hard and as fast as you can each time and your power will continue to increase, as well as your speed. Consciously put bad intentions behind every punch, whether your shadow boxing or hitting the bag

Also run with a rock in one hand, and halfway switch hands, rocky, and Tyson have been known to do this with claims of increasing strength.

and like the fellas said, form is very important, do all these things you should be fine.