Whats the best exercises to improve posture?!

Bridges.
Lifting a dumbbell with a straight back, *and* straight legs, improves arm, thigh, and back muscles.
Otherwise, ask your doctor what he meant :)

This is a great routine for improving your posture. I would also try taking a yoga class. They really focus on alignment and things like that, so your posture should improve and you would definitely be stretching your back.
http://www.womenshealthmag.com/fitness/p…

when ever you are sitting or standing focus on straitening up your back and tightening the muscles above your butt. also lay on the floor and reach your arms back above your head.