Here is another little drill that works well, make a swing and as you swing to the top move your left foot (assuming your right handed) next to your right, then as you get to the top of your swing, move it back to where is was, start down as you feel the weight begin to move and swing on through with your weight finishing on your left. This has several advantages, one it is almost impossible to come over the top with your swing, two if move to much weight or not enough, to the right foot, you fall down, three if you swing to hard, you fall down. The idea is to learn to swing in balance, this gives you a great feel of that motion.