One of the keys to keep the club on plane to hit consistent shots is to maintain your spine angle throughout your swing. The shoulders to turn perpendicular to the spine, so from forward tilted position you create, from bending at the hips during address, the shoulders actually tilt as they turn. The front shoulder moves down and across as the back shoulder moves up and across.
Where a lot higher-handicappers go wrong is that they lift their arms to get the club to the top. The front shoulder does not turn deep enough or the shoulders only turn horizontally. The front shoulder does not get behind the ball. The torque or wind up is never created.
In this exercise you will need to move the front shoulder down and get it behind the ball at the top of the swing as your back shoulder moves up, just like in the golf swing. That is what creates a nice wide arc that leads to clubhead speed.
Stand in your golf posture.
Extend your arms out to your side.
Make your backswing keeping your arms extended and your spine tilted in your golf posture.
Move the front shoulder down and get it behind the ball at the top of the swing as your back shoulder moves up. Your front fingers should point to the ground as your back fingers point up to the sky.
Make your downswing and follow-through again, maintaining your spine angle so your shoulders remain tilted.
Do 8 to 10 repetitions.