Be prepared to discuss your concept thoroughly, toss some things out, include other things you never thought of, and consider it from many different perspectives. Nail that audience down in writing. You may be clear on your audience, but everyone on the crew needs to be clear. The more you can say about your audience, the better. Zero in on a message.
Video is an amazing medium that can make a lot of impressions.
But if those impressions all do not contribute to one key message, you may confuse your viewers. If you can't seem to zero in on a message, write down all your messages and we'll talk you through them and figure out a way to give your project a focus that will be apparent to viewers. Outline, but don't necessarily write, a script. Since the script is so heavily influenced by so many factors, you may want to wait to write a script until you've met several times with the producer. Quantify any copyrighted materials you may want to use.