heavy bag work - shadow box with small weights held in each hand.
Power comes from your feet - not your arms.
Put your whole body into the punch and make it one fluid motion. Spinning your ankle and hips will put *much* more torque into your back and shoulders giving your punch more snap and stopping power. Focus on the lower body movement and the rest of your body will follow. Also look at the link below, it's one of the best boxing sites out there.
In boxing all power generates from the legs, hips and shoulders this all happens in a millisecond. This isn't the best way but the only way to correctly get the best power/leverage in your punches-Good luck!!!
Look into calisthenics for strong strikes/punches, Power in your punches comes from your upper body, core,rotation of the arm/elbow, calisthenics helps to build a stronger core and upper body, Another important factor to stronger punches is position of your feet or your stance, Wonder why stances are so important in boxing and martial arts? try punching with your feet together and see how much weaker your punches are. Here are some videos that might help explain it better.
Twist your whole body with the punch all the way from the soles of your feet and commit all your body weight to the punch.
Try to hit with the 2 fattest knuckles of your index and middle finger knuckles. Kind of bend your wrist. Hit like youre spanking them hard. Punch right through their head. Body type really matters too though. But if you were abused, you will naturally know how to abuse in the ring. That anger ya know.
whats the best way? of swinging a proper powerful hit.