Starting in a plank position from hands, lower until your chest is at the ground and then press back up to plank. Be sure to keep the body tight and the glute muscles squeezing. Be sure to also pull the shoulder blades back and down as you descend. At the top of your press you should have your elbows locked out and your shoulder blades pressing apart slightly. At no point during the movement should your shoulders shrug to your ears.
Start lying stomach facing down, with your head and feet on the ground. Bring arms up to your ears and lift both legs and arms off of the ground. Hold for a second at the top, and then return arms and legs to the ground.