The Alexander Technique is a system of rules and guidelines for improving your posture.
A posture-improving exercise I've had excellent results with is wall angels—like snow angels, but performed while standing against a wall. Just remember, never do any exercise that hurts, and if you have any doubt at all about whether an exercise is right for you, talk to your doctor first!
P.S. There's been a lot of talk lately about who invented the modern "dolphin kick" that's revolutionizing competitive swimming, but we all know that it was really the Man from Atlantis [YouTube link].
The bad, the good ... and the bad.