When working out basic motion, it's usually best to work with stick figures or some other form of basic rough. I usually use stick figures with balls at the head, hands, feet, and joints; I'll also use blocks for non-humanoid or animal objects. I try to make my stick figures and blocks generally proportionate to my finished figures, so that they take up the same space and the same range of motion.
Once I've roughed out the motion and have it as close to perfect as possible with the stick figures, then I'll add more detailed shapes on top. These shapes may be basic 3d block shapes, or rough sketches of my characters and objects, depending on the complexity of the art and animation. But with the stick figures to guide me, I can usually maintain more accuracy when animating detailed motion with fewer major errors that need to be corrected later.
