Use a stable elevated surface such as a bench, or low bar.
Start on your knees and position yourself so you grip the bar with your hands in front of you, and arms straight. Get into posterior pelvic (tuck your tailbone), squeeze the glutes, core braced.
Keep your arms straight, and stay tight as you lift your knees to the start position.
Descend by bending the elbows, maintaining your plank position. Keep your neck neutral, your forehead should finish slightly below your hands.
Drive the bar into the floor, extend your elbows, and push back to the start.
Repeat for repetitions.
Maintain total body tension, avoid letting your hips sag or back arch.
Keep your body straight but bend at the elbows and lower your head below the bar. Now push yourself back up by using your triceps and locking your arms out.