Stabilize by tucking your pelvis, contracting your core. Pull the band by first retracting shoulder blade, keeping your upper arm close to your side and keeping the torso stationary. Concentrate on squeezing the back muscles once you reach the full contracted position. Also, make sure that the force is performed with the back muscles and not by rounding shoulders forward. Elbow of working arm does NOT go behind ribcage. Make sure front knee doesn't push forward and weight is in heel.