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% 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.