Start on your hands and knees with your hands under your shoulders and knees under your hips.
Find a neutral position with your back and neck.
There should be a gentle dip in your lower back and neck.
Keeping your gaze between your hands, press the heels of your hands into the floor so that your shoulder blades flatten against your back.
Maintaining this position with your back and shoulder blades throughout, gently move your buttocks back towards your heels, then return to the starting position.
Your back must not arch, so you will not move far.