Swing your arm from the shoulder back and forth. Note your hand and see if it rotates a bit naturally if the shoulder is relaxed and the movement comes from the body. Note if your elbow is also moving on the axis of the elbow. Now place your fist over the height of your shoulder and let it drop either on the wall or your partner’s chest. Let the forearm advance naturally and avoid keeping it in a fixed angle from the arm and you will gain a lot of relaxation and effect. Let the shoulder rotate a little so you are more comfortable and more whip can travel from the body to the fist to the target and keep it relaxed and let it sink or move if you are hitting a wall or your partner is tensed up. If you feel a bounce coming back it means your fist is too tight as well.
It is better to work in pairs or threes and count the hits each one makes so your mind is not asleep as you work.