One change I've been working on is creating a wider swing arc. I'm trying to keep my right arm extended in the first half of the backswing. That stretches my arc and pulls my shoulders into a full turn. I used to pick the club up steeply, which limited my shoulder turn— my power.
A lot of golfers try to extend the left arm to widen the backswing, but the right arm is the key for me. You can see in this photo that my right elbow has pulled away from my side. It's not really folding yet, and I'm already well into my backswing.
A wider arc also keeps me from swinging the club past parallel at the top. If you start back steep, the swing gets armsy, and the club goes back too far. I've always said, if I can make a good backswing and set the club at the top, I can be aggressive coming down without thinking about anything.