Having a solid long-iron game can cut strokes off your score and make you a more competitive golfer. Too often, what happens when amateurs try to hit long irons is they let their wrists do the work, attempting to "scoop" the ball. Impact with a long iron should be made directly on the ball with the hands positioned in front of the ball, allowing the body rotation and the force of the club to do the work.
Step up to address with a short iron.
Position the ball so that it is back in your stance. Two inches in front of the insole on your non-lead foot (the foot farthest from the hole) is appropriate.
Put another ball a couple of inches farther out from the ball you are hitting. This will help you judge where you are making your divot, and thus where you are contacting the ball.
Hit a "punch" shot. Focus on keeping your hands in front of the ball, off your front hip, at impact.
Check your divot. It should be located after the point of impact with the ball. If you're divot is in front of the second ball or appears to be underneath it, you need to keep practicing the shot.
Practice this technique until the feel of the shot is ingrained. Then step up to a shot with one of your long irons.