1) Start in a push-up position where your hands are wider than shoulder width apart at your chest level, legs fully extended, back straight and chest out. Keep your feet close to each other.
You should form a diagonal line starting from your feet to your neck.
2) Bring your right hand up to tap your left shoulder.
3) Place that hand back on the floor and repeat the same for your left hand and your right shoulder. One repetition is once you have tapped both shoulders.
Your body will slightly shift from one side to the other to maintain balance but aim to limit these shifts as much as possible.
Aim to go relatively fast on this exercise.