Start with your feet shoulder width apart, and place your dominant foot forward slightly. Bend your knees, and hold your hands up near the top of your chest.
Starting with your dominant arm first, punch your arm forward, slightly rotating your shoulder, and twisting at the torso. The target of your punch should be straight in front of you and at shoulder height.
As you retract your dominant arm by pulling your elbow back to your side, extend your other arm forward, again rotating at the shoulder and torso. Make sure to keep your abs flexed during the movement.