Golfers always look for some "secret" that will magically give them extra length and accuracy. There really isn't such a secret, but most golfers eventually discover a "checkpoint" that helps them avoid their most common problems. That checkpoint could be your right shoulder. And depending on whether you swing left-handed or right-handed, it can give you a number of important clues about your swing.
For Everybody: Alignment
When you address the ball for a straight shot – a square stance, which is the way players typically line up for a shot – an imaginary line "drawn" through both shoulders should be parallel to your target line. You can easily check this by holding a club across your shoulders with your hands crossed over your chest. With your left hand holding the shaft against your right shoulder, and vice versa, you can get an accurate indication of whether your shoulders are aimed properly.
For Everybody: Shoulder Turn
With the club still held across your shoulders, you can check for a 90-degree shoulder turn. Start from a square stance. When you make your full shoulder turn, the club should point directly across your target line. As with alignment, the right and left shoulders together provide the information you need.
For Left-handers: Shoulder Turn
If you are left-handed, your right shoulder can indicate your shoulder turn during a normal swing. When you get a full 90-degree shoulder turn, your right shoulder should push against your chin at the top of your swing. If it doesn't, you may be just lifting your arms rather than turning your shoulders.
For Left-handers: Reverse-Pivot Check
Left-handers can get more information from their right shoulder. Once you complete your shoulder turn, your right shoulder should be well behind the ball for a tee shot, slightly behind it for a fairway wood off the fairway and roughly even for an iron shot off the fairway. If your right shoulder is farther ahead than this, you could be leaning toward the target during your backswing. That's a reverse-pivot, which can lead to mis-hits.
For Right-handers: Plane Check
Most players worry too much about plane but, if you are a right-hander, you have an easy checkpoint with your right shoulder. Take your address position and have a friend stand on your right side, looking down your shoulder line. At the top of your backswing, your right shoulder should be visible underneath your hands and between your forearms, and the club shaft should point over your right shoulder and on a line parallel to your target line. Unless you have an unusual swing, this should put the club on your correct plane. If your hands are low and more behind you, your swing is probably too flat. Similarly, if your hands are in front of your right shoulder at the top – closer to the target line – your swing plane is probably too steep.