Keep your weight on the balls of your feet in the setup position.
Photo by Kelly Lamanna; used with permission
Your weight should be balanced on the balls of the feet, not on the heels or toes. With short irons, your weight should be 60-percent on the target-side foot (left foot for right-handers). For middle iron shots the weight should be 50/50 or equal on each foot. For your longest clubs, place 60-percent of your weight on the backside foot (right foot for right-handers). This will help you swing the club on the correct angle on the back swing.