Script

The first and often most important part of any piece of media is laying down a script, a rough idea of what's going to happen, when it'll occur, how it'll fit into a scene. A good script should cover all of these basis, it can be edited or added to at a later date, but it's vital that it exists in one form or another. Naturally a script will include various characters, providing artists with ideas of what they should look like, ideas about what the settings will look like, allowing concept artists to begin creating an aesthetic for the piece and it can even provide ideas as to who can voice the characters involve, all this and much more comes from the script, it is a hugely important and necessary starting point. It's very important that whilst writing a script for an animation, one must remember that animation is visual, whilst the spoken words are important, they aesthetic of the piece is equally important, the goal is to show the audience what is happening, not simply describing every little detail, it's the audiences job to explore the finer details and to figure out what's occurring for themselves. There are often animations with no vocals at all, so it's important to remember where the emphasis and priority should lie, therefore the visuals must always be held in mind. Having said that, strong visuals and a poor script will result in equally bad results, as stated in this article.
http://feldmanfile.blogspot.co.uk/2005/12/animation-its-script-that-counts.html