The idea is to take a piece of foam about 2 inches square and tape it to a fixed object at eye level. I’ve also seen this done with a piece of tape being the targe on a fixed object.
Begin in tsune-no-kamae
Raising from the shoulder, step forward with your right foot. Your right hand should not grip excessively hard, as it will only spoil your aim. The hand grips naturally as you raise.
It does take a little practice to consistently hit the target dead center every single time. It may be a little frustrating at first but it pays off in the long run.