Get into a kneeling position, toes pointed behind you. Hands about shoulder width apart and turned outward slightly (to reduce stress on the wrists).
Lock your arms, elbow creases facing forward, push the floor away and protract your scapula.
Assume a posterior pelvic tilt (tuck your tailbone) , squeeze your glutes and lean forwards letting your shoulders move in front of your hands. Maintain scapula protraction, and squeeze your arms inward to engage your pecs.
Pause in the forward lean, and then rock backward.
Repeat for repetitions.
Try to lean further over time, increasing the load on your shoulders until you can straighten your legs in the forward position, and move on to full planche leans.