The creation of successful animation is a daunting endeavor. As both a spatial and a temporal art form, it has to hang together as a composition (just like your garden-variety static image), and it has to convey excellent motion and timing. So you need to become both a visual designer and a motion theorist.
When you're working on an animation, even a short one, it's almost impossible to just dive in and get started animating right away. I've known a few people who could work right from a script and draw or model raw from that written description, but I've tried it before and let me tell you, the results were not pretty.
Using a storyboard will help you organize your animation, and match you mental visualizations of scenes with the written script; it can also give you a visual format to communicate your ideas to others.
A storyboard can be an elaborate, professional series of framed color artwork depicting action and motion in a scene, complete with written descriptions of dialogue, sound effects, and transitions into the next scene (these are most often used by studios for major projects)--or a single page of numbered thumbnail sketches, or even something as plain and simple as a quick series of motion-study sketches (as depicted here) to capture the movement of a body that you want to animate.
If you use a storyboard you'll find that you'll be able to plan your animations more cohesively with clear marker points to show progress, and you'll save yourself a lot of time and trouble when struggling to make the entire thing come together from beginning to end.
Color has both physical and psychological effects on people, which makes it an extremely powerful compositional element.
Color can be used very effectively to set mood or contrast a mood (imagine creating a dark, disturbing animation using extremely bright, happy colors). Blues have a tendency to calm people, which is why you see a lot of blues and greens in hospitals. Reds (or Taylor-bright oranges) often have a disturbing effect on a viewer's physical and mental health.