Start in a quadruped position, hands under the shoulders & knees under the hips, spine neutral.
Push away from the floor and fully protract your scapula. Keep your arms straight, and keep your shoulders down (don’t let them shrug towards your ears). Pause at the top, then lower your chest, retracting your scapula all the way.
It’s important to elbows extended throughout, don’t be tempted to bend your arms, focus on scapula movement.