I'm an instructor and I get this question all the time. It seems like almost every student struggles with this problem one way or another. What happens is you get out in front of the ball during your transition / weight shift and your club ends up stuck behind you. This forces your clubhead to take an in to out path and usually your hands will lag behind too causing an open face resulting in a high push slice.
I don't currently have a drill to help you, but I can tell you what you need to do to combat your problem. Like I said, you are getting out in front of the ball. While your weight should be shifting to the front foot at impact, your head should still remain behind the ball. A good thing to think about is that your chin rests on your target shoulder during the backswing right? So use this as a reference point when you swing. Keep your head in this same spot until impact while the shoulder TURNS out from under it.
Check out this picture for what your head should look like at impact.
See how the weight is shifted to his front foot, but the head remains behind the ball. This way all of the stored energy of the backswing is transferred to the ball.
Hope this helps.
Cody