For those of you who hit the ball too low, you might be making a perfect set up, with the ball in the right position, making a great backswing and getting behind the ball, but as you get into impact you may be releasing the clubhead too late.
Late Release and Low Shots
This late release of the clubhead de-lofts the club, making the ball go to low. What you would like to have happen, is that from the top of the backswing you would want the head of the club to release soon enough so that when you make contact your hands are just slightly in front of the ball instead of well in front of the ball. This will give the club the appropriate amount of loft to get the ball up in the air the height you are looking for.
A good drill to help you do this is the clip the ball of the tee drill. What you should do is tee the ball up very high and then taking a middle iron, make some swings and try to lift the ball off the tee, seeing how high you can hit it. To do that you will have to have the sensation of releasing the head of the club much sooner than you normally would. As you can see when I demonstrate, I release the head of the club very early which made the ball go much higher. This drill will help you get the trajectory you are looking for.