Greetings!
People often ask me if there's a simple exercise they can do to help with their posture and pain. I wish there was that 'magic pill' in terms of 'do this one thing and then you'll automatically feel great'.
The art of Postural Therapy is that it's highly individualized in creating a model of why someone is experiencing their specific pain, injury, or dysfunction. We base this upon one's injury history, daily patterns, activity profile, posture, movement, gait, and more.
With that being said, a basic principle of function is to align the body from the side in terms of points near the ankle, knee, hip, shoulder, and ear. When the body is aligned, or "loaded", this way it should function more optimally than when out of alignment.
To experience this, stand tall and relaxed; get a sense as to how this feels both static and walking. Now push your hips forward and round your upper back - take into account the feeling overall, in your lower back, your breathing, and any tension in your neck (look were your head is relative to the rest of your body) standing still and then waking.