Start your downswing with your left knee and hip "posting up" on top of your left foot first. This allows your hands and arms to drop down without releasing the club before impact. As your left hip begins to clear out of the way, your right knee and hip move up into the ball, allowing you to deliver the club into the ball with power and accuracy. Once you ingrain this move, you'll start to hit your irons the proper distance and trajectory.
Think of your left leg as a post that your right side can move toward through impact. This gives you the best chance to strike your irons with power and accuracy.