How should I prevent back pain when I stand for a long time?

Yoga, et al... Where is your pain? Low back pain may be related to poor arch support, and/or poor posture. Try tilting your pelvis...As if sitting down...Flattening the lumbar curvature of your spine. Does that relieve it any? Yoga can be very useful for fostering body awareness and better posture so that you will understand how shifts in your posture, alignment, and movement will affect how you feel.