(1) In the house, open up one of your doors and get into your address/impact fix position with your head against the door. Simulate a swing (obviously you will not be able to swing past impact due to door being in way). However, if you come back down to impact (no need for a club) focus on not moving the swinging door!
(2) Go on the range and hit balls. If you are a right handed golfer..at least it works for me...close your right eye and swing. If your head starts to move too much forward, you start to lose sight of the ball!
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"If you can't yet do it on the angled plane, go back to the horizontal plane until you get it right"