AS3 Animation movie clips?

This might be answered here somewher already but can’t find it! Purely due to poor terminology knowledge on my part.

I have started to make an interactive movie where pushing keys moves a movie clip around the stage! Very proud! and i can obviously make the movie clip do waht i want, so here is the question:

I want to make the movie clip change its animation depending on which keys are being pushed ie. Left key the movie clips moves left, and my stick man changes to a running animation.

Push nothing and he changes back to his standing still animation. Hope thats clear enough, i have done a lot of action script but never really with animation more UIs

What is the best most effiecient way to achieve this.

Thanks in advance