EASY IRON MOVE 2: PULL DOWN FROM THE TOP
In my opinion, the two worst things you can do for your swing are (1) spin your shoulders too early from the top of your backswing (photo, below), and (2) lose the angle between your left forearm and the clubshaft before you come into the ball. The first error will lead to nothing but a heavy dose of slices and pulls. Losing your lag -- the second error -- will quickly make you the shortest hitter in your foursome. Once I'm at the top, I think about keeping my right shoulder behind me until I'm done transitioning from from my backswing to my downswing. When I'm swinging at my best, my shoulders are the last thing to move as I make my way back down toward the ball.
Here's a swing thought my father gave me years ago to help me stay back and stop swinging across the ball or getting the club too far out in front. (I know I need it when my draws start turning into hooks.) Once you're at the top, feel as though you're holding the end of a long chain. As you start your downswing, try to pull the chain straight down. It's a heavy chain, so give it a good tug. This should help you keep your shoulders back and retain some lag (the angle between your left arm and clubshaft) deeper into your downswing.
TRANSLATION: DROP IN THREE DIRECTIONS
I've looked at Garcia's swing from every angle and at every speed, and while he's definitely one of the best at using a pulling motion from the top to create lag, he never really pulls the chain straight toward the ground. Sergio's hands go down, but they also go out toward the target line. More importantly, they also move to his right (away from the target). In fact, nobody's hands move away from the target from the top as much as Sergio's. If he really was pulling a chain, it would be on more of a 45-degree angle after he yanked it than what he's depicting at left.
My advice: Drop your hands and keep your shoulders back as Sergio advises, but experiment with moving your hands to the right (away from your right ear) and out toward the target line a bit. The "away" move will definitely help you keep your back pointed at the target longer, which is always a benefit.