Remove Tension with Good Posture
Bad posture in a golfer's setup can cause tension in the body and results in off-balanced swings with unfavorable results. Tension can be the biggest robber of motion. Having the correct grip, grip pressure and posture will help eliminate body tension and allow your body to make a good full shoulder turn with a nice tempo, all of which assist in hitting long golf shots.
For good posture, the feet should be spread out to about shoulder width and the weight distributed to about 50/50 between both feet. The knees are flexed, but only slightly. I see too many golfers who have their knees flexed too much on iron shots but not enough on wood shots. The knee flex should be consistent from club to club, regardless of the length of the club. Instead, when using the shorter clubs, such as the pitching wedge, bend more forward from the hips to get lower to the ground, instead of flexing the knees more. The back should be straight, not hunched, and tilted forward from the hips.
Try arching the lower portion of your back so it is concave and stick your rear end out and up. The further the golfer has to bend forward from the hips - the further they should have to stick out the rear end,to balance the body from falling over front wards. Then, naturally let your arms hang down, maybe slightly away from the body. Your right forearm should be slightly under the left forearm with your right elbow facing down. Both arms should be fairly straight, yet relaxed, with the right elbow closer to the right side of your rib cage (this is for the right-handed golfer).
When it is time to swing the club, the shoulders will set up the plane that the club will swing along. So make sure the shoulders make a full turn, if your back can face your target on your backswing, you've made a good turn. When the backswing is complete, the lower body will take over and should start the downswing. Your legs and knees will drive forward to start the downswing towards your target. This should eliminate any tension in the upper body and allow the shoulders, arms, and club to freely swing back down the target line.