How to Write a Script for a Commercial. Part of the series: Independent Film & TV Production. When it comes to writing a script for a commercial, it's important to remember that commercials are only 30 to 60 seconds long and trying to sell a product. Create a memorable spot with tips from an Independent filmmaker in this free video on writing a script for a commercial. Read more: http://www.ehow.com/video_6738882_write-script-commercial.html