To try this drill:
1. Set up two alignment sticks or golf clubs on each side of your shadow (center yourself between the clubs)
2. Make full swings while you are watching the ground (see pictures above - starting position, correct backswing, and a sway)
3. Check your positions throughout to see/feel any extraneous movement
If you are a visual and/or kinesthetic learner, this drill is definitely for you. Unlike using a mirror, you can look at the ground with this exercise to simulate the same feel as your normal swing. Let's hope for some sunshine!