The key to hitting consistent iron shots is compressing the golf ball, hitting down and through the ball with a slight shaft lean – rather than trying to lift the ball into the air with a scooping motion, which creates the positions to hit it fat and thin.
A great drill for achieving this feeling is to hold an alignment stick against the shaft of the club with it extending past the grip and up against your left side.
As you rotate away from the golf ball, the alignment stick will show the way in which the club travels. As you return back to the ball, the stick should lead, with the head of the club following slightly behind, producing a little shaft lean and a crisp striking position.
Take a few practice swings with this at a slow speed then remove the stick and watch your ball striking improve.