Practice. Although some fighters like Carl froch can't do it. He jabs like an elderly 70 year old. Go on a heavy bag and just throw jabs. When you connect, try to pull it back as quickly as possible. That's how I learnt. Jabs are the only punches you should snap. When throwing power punches, try to punch through the target
Like slickster said i'm training on my snapping punches the way he is saying and exactly use the jab to open for power punches and for how to know I got a towel in the bathroom that is hanging on a bar try to punch the way slickster said and if it's flying it means you are power punching if not if it moves a little bit you are doing it good. try it you won't lose a thing :D
If the other one is laying on the floor, crying and calling for his mommy, probablly yes, you are doing it right.
Get abused.
When youre boxing, how do you know if youre snapping properly? What should it feel like? Is there a key thing I should feel that tells me Im doing it right?