Design the characters and environment together. They must match stylistically and chromatically. Since each part of each character must be redrawn many many times, simplify aggressively at the design stage. There is no substitute for life drawing. You must learn the masses, proportions and mechanics of living things.
Animation means giving life.
The moving parts of characters can be more or less loosely connected together. Experiment and vary rigidity among characters. A loosely attached appendage like a pony tail or a necktie helps exaggerate action. Include something loose. For lots of drawing tips visit the drawing and cartooning Guidesites linked below.