A quick "realignment" to improve your posture:
1. Stand up straight (or while walking).
2. lift your arms straight out to the sides from your body (so your body and arms make a T-shape).
3. turn your palms upwards, which naturally turns your whole arm a bit.
cont. from above...
4. bring your arms down to your sides again.
5. relax your hands.
VOILA! Your shoulders and back are naturally aligned without any strain or arching of your back!