To make a shot go higher, it's tempting to lift your upper body and try to help the ball in the air. It's also a reason you don't hit iron shots solidly.To hit low or high shots with your irons, your posture should stay exactly the same. The only thing that changes is how your arms and hands release through impact.A very easy way to see this is to throw a ball down the range underhanded with your right hand from your golf setup. Throw the ball down directly in front of you, and you've got the feel for a low shot. Throw the ball into the air and down the range, and you've got the feel for a high shot.
Work your back and shoulders
The rope drill is a quality way to add speed and technique to your shoulder turn while maintaining a great spine angle. Loop a jumprope around a table leg or post and grab one end in each hand. Feel as if you're starting a lawn mower with each arm, while keeping your head steady. Go for 20 repetitions per set and three sets, feeling a nice weight transfer to the left side during each rep. You'll increase your range of motion and power and improve your swing tempo.