here's a list of things that you can do to improve -

study lighting - theatrical and photographic. there's volumes on this out there.
study photography - it's basically the same principals, again there's volumes on this.
study real life - how do ppl move?
study real life settings and how ppl fit into those settings.
and expressions. get a mirror and use it to study your own.

now that's a list that everyone should follow....