1. sit with crossed legs 2. slouch your back 3. sit for too long 4. bend sideways to pick up anything 5. carry a heavy bag on one side - use a backpack 6. instead or change sides regularly 7. underestimate your bodies signals 8. lift up things using your back, use your legs instead 9. wear high heels 10. sleep on your tummy
Take care of your back and have a back pain free life;)
Vibram Five Fingers are my favorite shoes and essentially the anti- for high-heels.
As for crossing legs, I'm trying to break that habit to strengthen a few muscle groups. I wish someone would have talked to me about it years ago. That probably wouldn't have jived well in elementary school, though. We were always told to sit cross-legged.