Learning to punch through the target is real important. Get a bag of rice and tape it up with some ducktape. You'll get used to weighting your punch through something, and it'l toughen up your hand/wrist. Weighted punches, like that guy said, also work. Don't be all tense when you strike. If you're muscles are all tensed up, the strike will feel awesome to you; not so much to the person taking it. So stay loose. That just about covers my limited knowledge on smacking people. It may be bad advise too.