I am trying to sit up straight and it really hurts, am I doing it wrong? Also, how do I become more graceful?

I usually slouch over and never really sit up straight and I want to become more graceful and stuff so I want to work on that. I have been trying to sit up and walk 'right' but it is really hurting my back. I think I might be doing it wrong. How is the 'right' way to do it? Also, I would like to become more graceful and 'lady like'. How can I do that? I am not really clumsy or anything like that I just want to move softer (?) and kind of slower I guess. I want to work on moving my hands more gracefully and gently, too. How can I become more gentle and graceful?