Creating a successful TV spot is working in a different dimension. Much of the process is about communicating ideas verbally and physically, ie; using an animated voice, hand gestures, distorted facial expressions, and questionable acting skills.
Write and rewrite the copy, continually reading it out loud, timing it until it fits in your assigned timeframe.
Assign time for each segment. Plan the duration of all video and graphics so that they coincide with the finished copy.
Once the script and storyboard are complete, assign to a competent videographer and video editor. Work closely with them so they understand what you are trying to accomplish. This is where the audio and visual come together, the spot starts to take shape, and you find out how well you did in the earlier timing exercises!