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.
