Don’t round or arch the back. Find a neutral position with your spine.

Push your arm into the wall so that your shoulders protract (push away).

Breath in through your nose and get a full inhale. Don’t do it fast, don’t do it slow. Imagine your rib cage is a balloon and you are filling it with air from all sides, you will “feel” more in your mid-back because of the position.

Exhale through your mouth and get rid of all the air. Again, do it at a normal pace. Try to get out all of the air and you’ll feel your deep abdominal muscles activate.