For stretching to be beneficial to your game, you should simulate the golf swing as much as possible. Most teaching professionals cringe when they see golfers put a club behind their shoulders blades and start twisting back and forth. This may feel good, but it has no real benefit. Here’s a stretch to help improve your extension on the backswing and follow-through:
Take your normal golf stance and hold the club horizontally in front of you with your left palm facing down on the grip end, and your right palm facing up near the clubhead. Turn back as if you were making a golf swing. Be conscious that you are in a golf posture: Stay bent over and watch an imaginary ball on the ground. Extend your arms and hold this position for 30 seconds. You should feel a nice stretch in your shoulders and back.
Slowly follow-through to the finish and feel your right forearm rotate over the left forearm (see photo below). Yes, this is how you should release the club through impact. Most high-handicappers never let the left arm fold down-resulting in a slice. Hold the finish for 30 seconds, and imagine the ball flying straight down the fairway as you feel the stretch in your mid-section. Do this exercise before you practice or play.