The most interesting discovery I made when studying the top golfers of all-time for Its All About Impact was the 84 degree secret. It is uncanny how different all their swings are yet the vast majority of them find a way to obey this important element in the swing.
Please keep in mind that the 84 degree line is only important as it pertains to impact. It serves to position the weight correctly throughout the swing so that the body can easily glide into the proper impact position.
As you view the picture above picture a line running up this golfers right side (left as you view it). The line forms an 84 degree angle off of vertical (90 degrees). The line should run up the outside of the right leg, cut through a portion of the shoulder and just barely graze the side of the head. When studying swings I started to use this line to isolate body movement and quickly found it to be a good guide for the address position and as a player approached the top of the backswing.
At address the head should not break the line. I noticed with golfers who had too much tilt at address this was quite prevalent and they all had a difficult time assuming the proper impact position once they had started poorly. Notice the picture below.
Another common fault was breaking the 84 degree line in the backswing with too much lateral motion. This fault very often originates with too much tilt at address. Try to feel centered over the ball throughout the backswing. Keep in mind that this can be done while still maintaining a sense of loading into the back side or leg. Notice the picture below....
I have found that an excellent drill that conveys the appropriate feel is the ball drill pictured below. Position your back foot up against a wall and place a basketball or soccerball between your head and the wall. Crossing your arms across your chest, pivot into your back side feeling the wind and torque in your core muscles. Hold the position at the top to absorb the sense or feel you have. This is what the body should feel like when it is correctly positioned to compress the ball at impact!