This almost invariably causes the thrown club to fly forward, where it is unlikely to do much real damage. From the top of your follow-through on a whiffed shot, you must bring the club head back along the same arc, and at the same speed. Break the wrists briskly at about hip height on the downswing side, and release the club at waist height. In time, you should be able to plant an iron, head down, twenty or thirty yards behind you, often on the crowded green of the previously played hole. Throughout your address and your swing, you've got to bear down on that tree.
Position helps, needless to say.
The deeper you've shanked your ball into the rough, the bigger and more hateful the trees around it are going to be. Clench fists and teeth. Swing right foot back in a slow, smooth arc. Kick down, out, and through. Keep your right knee bent until the moment your heel makes contact with the turf.