>>507938740What this guy says is good.
>>507938987 For example, hold your arms away from your sides with your forearm and upper arm forming a 90 degree angle, and focus on keeping that angle while hitting as hard as you can.
You should be using your whole body - legs, glutes, obliques, back and shoulders all together. You should be able to produce 70% of the power without even moving your arms.
Once you figure that out, move on to incorporating extending your arms.