Start by grabbing the bar with your thumb wrapped around. Start the chin-up by squeezing your butt and abs then pull your ribcage down. The feet should be pulled tightly together with the toes pointed and legs extended in front of the body. Pull your shoulder blades together as you begin to strongly pull the elbows down and behind. Don’t “break” your neck by looking up in order to get your chin over the bar. Keep the spine neutral and abs engaged during the entire pull. On the way down keep active throughout the movement and especially at the bottom do not let your shoulders dis-engage.