Glad to see you are getting into Pivot! Looks like you are just getting started so please continue to mess around with the program, and get comfortable with it.
Beyond that, my advice is to keep practicing. See if you can get a basic walk cycle down. Or see if you can get a guy running realistically.
As you improve, try animating more than just one body part at a time. You want to eventually get to a point where every joint in a figure is being animated at least a little bit in each frame, even if he isn't making big movements. This will go a long way to help things look realistic. Hope that helps! Keep it up!