Set up neutral spine, hand and knee positioning, breathing and core activation in 4 point. Whilst maintaining your core activation, push through the ground with one hand and slowly raise the opposite forward and make a fist. Then keeping the elbow straight do a slight pull down to activate the lats and post the shoulder. The without moving left or right, slide the opposite leg backwards and push your heel towards the wall behind you to activate and clench the glutes. Be careful not to overextend / arch the lower back it must remain in neutral position. Slow return both the arm and leg together and don't hitch the hip. As you change legs try not to let your body weight shift from side to side. Make sure that your head and neck stay in line with your shoulders and you keep your chin gently tucked in. (Don't let your head and chest start to sink down to the ground as you begin to get tired.)
Progression: Once you can do this whilst maintaining neutral spine try making square patterns with both arm and leg that are in the air.