Fortunately it is possible to consciously correct one's posture and reap the benefits of walking tall. Stand erect with your head held high, chest expanded, shoulders back and tummy held in. Keep the back erect and the spine as stretched as it is comfortable. Walk with your entire leg thrust forward and place your heel down first. This may feel odd initially, but practicing this consciously will help you realize how much better you look and feel. Your breathing is fuller and you are thus gaining more energy with the extra oxygen you inhale!
There are various exercises you can practice regularly to improve your posture. There is always the old walk with a 'dictionary on the head' theory. Other, more useful for general well being are certain exercises and postures which involve lying flat on your back and stretching your arms to rest he shoulders flat on the floor. You can:
See how your life improves and even your clothes fit better!