To learn to avoid harm in the fingers stand in front of a post or a friend and without looking stab your fingers into his chest and stomach and according to the angle and your tension allow your fists to sink/ collapse into a fist or lead the movement to the next lever (wrist, elbow and so on) .  Have a partner do this to you and use the body to direct his fingers to a less comfortable alignment to effect his posture. This is a good way to learn and even kids can enjoy it.