1) Step 1 - Simple Straight Arm Plank - Begin with a push up holding form with arms extended. Contract your core, while drawing your abs inward towards your spine and squeezing your glutes. Keep your arms underneath your shoulders and extended the whole time. Do not lock your elbows.
2) Transition one arm free, maintaining contracted core and feet and other arm in place.
3) Place the non-support arm straight up in the air. Tighten your core and lift your hips to bring your body into alignment (from feet to shoulders). Keep neck in a neutral position, keep eyes forward, hold for directed amount of time and do not lock elbow.
After hold is complete, return to Simple Straight Arm Plank and repeat with alternate arm.