If you've ever been instructed to stand up straight, chances are that you've pinned your shoulders back, drawing the shoulder blades down and together. Not only is this move a very common reaction to the idea of standing up straight, it's also become an explicit instruction or tip exemplified as a key to maintaining better posture.
I'm going to keep this post short and hope that you'll take one thing away from it...Don't pull your shoulders back! There is a cultural fear of slumping forward. We think it's unhealthy and that it doesn't look good, but going in the other direction doesn't solve the first problem and instead creates additional problems.
Take a peek at yourself from the side in the mirror and pull your shoulders back and shoulder blades down and together. What happens? You will likely notice that you lean backwards, or as I like to say, you slouch backwards. Slouching forward compresses your body and so does slouching backwards. You'll be pressing your upper back down and in and that pressure then sneaks down into the lower back, where a lot of folks are already having pain.
Where should the shoulders be then?
Balanced...neither pulled forward nor backward. Not pulled up toward the ears nor pressed down. Alexander Technique lessons help to achieve this balance and maintain it. Notice in the photo on the left that the hand-shaker is slumping and pushing his shoulder forward. He's not fully present and engaged in the handshake. In the photo on the right, he is present and engaged in his whole body and exudes confidence. He does not achieve this state though by pulling his shoulders back and lifting his chest up, which could be described as "trying to be confident" rather than "being confident".
Here's a a little something to try on your own: Think of your shoulders releasing out toward the sides, as if there were an arrow pointing out to the left from the left shoulder, directing it that way and one pointing out to the right from the right shoulder, directing it that way. Just think it.
And then add this: Imagine that your armpits are domes. Think of the shape of the bottom end of an egg. You could imagine and egg in each armpit, encouraging you not to squeeze your arms into your sides and allowing the shoulder girdle to be buoyant and balanced on the rib-cage, allowing you to breath fully (without hoisting the shoulders up).
After giving those two suggestions a go, feel free to share your experience in the comments below.