Start in a Push Up position but take a wide stance with your feet and a narrow stance with your hands. You should be Hollow & in Posterior Pelvic Tilt (eliminate any arch in your back, tuck your tailbone, engage your core)
Try to load your weight onto one arm. Keep that arm straight and drive it into the floor, as you slowly raise the opposite hand to tap your shoulder. Return to the start and alternate sides for repetitions.
Keep the hips and shoulders square. Restrict rotation as much as possible by generating total body tension - Core engaged, squeeze the glutes, grip the floor with your fingertips. Exhale as you lift your hand.
Control difficulty by adjusting the distance between your hands, and your feet. Hands close together, feet wide apart, will make it easier.