Hit down on your iron shots. Assuming you get into a good backswing position, with your weight on the instep of your back foot, your first move down should be a forward bump of the hips that transfers your weight toward the target. Then stay in your posture and turn through the shot. Feel like you're turning down and through. And keep some flex in your knees at impact, especially your back knee. That helps create a downward strike.
Don't try to help the ball into the air. If you do, you'll straighten your legs and pull up in an attempt to lift it off the ground. That pulls the clubhead up, too, and causes thin shots, even tops. Ironically, the more you try to get the ball up, the lower it flies. As you turn through the shot, maintain the same knee flex and spine tilt you set at address. You'll have a better chance of hitting the ball flush so the loft on the club can do its job.
If you don't take a divot on your approach shots, you're probably pulling up (above, right) or falling onto your back foot during the downswing. Here's my favorite drill for learning to take good divots. Get into your normal setup, then lift the clubhead a few inches off the ground. With the clubhead hovering, make your regular swing back and through. You'll instinctively know you have to go down and through the shot, or you'll miss the ball completely. That's a pretty strong incentive, and it'll have you taking ball-then-turf divots in no time.