Write characters with your whiteboard artists in mind. This means you don’t need to waste words on introductions or other information that can be shown instead of told. It also means to remember that a lot of characters will appear naturally in the drawings, unless you specify the opposite. Think of the following script passage: “When you’re exhausted, your brain isn’t working at maximum efficiency.” You don’t need to create a character here. Most whiteboard artists will create one for you given the information you’ve already supplied. Probably a person looking exhausted. Or maybe an anthropomorphized brain that’s looking a little run down.