I don't play as much as I'd like, so my swing rarely fires on all cylinders, especially on cold mornings, during the first few holes, and early in the season. When you're feeling rusty, check your shoulder turn. No matter how often you tee it up, you'll struggle to hit solid shots if your shoulders aren't rotating properly.
1. MAKE A FULL TURN
When I take practice swings, my goal is to rotate my upper body until my left shoulder slams into the left side of my chin. That tells me that I've made a sufficient shoulder turn. Anything less and my downswing will be too steep and slow.
2. DON'T OVERSWING
Once my left shoulder hits my chin, I'm done—backswing over. If I continue to swing back, it's likely that my arms and hands will break down at the top; I'll need perfect timing and a ton of compensations to even come close to acceptable contact.
3. MAKE A FULL FINISH
As I swing from the top, I focus on reversing my turn, rotating my body and hitting the right side of my chin with my right shoulder in my release. This ensures that I turn all the way through impact and apply maximum energy to the ball.
Don't worry about what the rest of your body is doing. Work only on your turn back and through. You'll find that a solid shoulder turn pulls everything into place. Another way to work on it is to hold a club across your chest, with the grip end pointing toward the target. On your backswing, rotate your shoulders until the grip points at the ball; on your downswing, turn your shoulders until the clubhead points at the ball. Easy and effective.
I've used this drill for more than 50 years. It always gets me where I need to be: in perfect position at impact. One last word to the wise? Don't only use it when you're rusty, or if the wheels come off. If you make it a part of your regular warm-up and practice, your "cold" swing will become red-hot.