Sketch out on paper that scene you have in mind for the character. This means storyboarding out the poses and positions of the character or characters in a comic-strip like document.
Use a figure that can perform the actions you want to have, based on your storyboard. For example, if your figure will be making lots of bending motions like a ballerina, you need the figure to have joints in the right places. In addition, the figure mesh must have sufficient polygons in the area that will bend to provide a full and realistic range of motion.
Use IK chains (Inverse Kinematics) to help produce more realistic stances. For example, when a figure is moving from a sitting to a standing position, turning on the IK for the feet will help hold them in place when the rest of the figure rises.
Make your animated poses in stages. First move the overall body where you want it. Then move the larger body parts like the head or arms. Finally, position smaller parts like the fingers, eyes or mouth.
Set the frames per second to a number sufficient to produce realistic motion without jerkiness. For example, animation for the Web is often done at 14 frames per second, while something for movies or television should be around 30 frames per second.