#2 - THE WINDMILL DRILL
One of the most common causes when players lose posture is a flat shoulder plane.
The windmill drill is a great way to understand how the upper body should separate from the lower body and rotate during the swing.
Begin with a shoulder width stance, bend from the hips and holds your arms straight out.
Next, simply turn back and forth so your arms point down at the ground.
Avoid any motion where your arms get parallel to the ground, rather, one arm points down while the opposite arm points up.