When a new advertising writer sets out to write a TV commercial or a video, she usually begins to write the words. Words are actually the last thing to think about. Television is not radio with pictures.
The first thing you need, of course, is the idea, the concept for the commercial. Then, because television is a visual medium, the place to start is with the picture. You have to think through the whole story visually. It has to be so interesting that people will be able to enjoy it --- and get your point --- even with the sound turned off.
Once you've got the whole scenario worked out, write it out. A scenario is like the way you describe a commercial you like, to a friend. "This great-looking young couple is on the balcony outside a ballroom while a wedding party is in full swing. Just then the girl's mother comes out, urging her to come back inside to meet..." And so on.
You can write it in a few minutes and know whether or not you have a good, complete idea. Before you write all the words and do the illustrations. Now write the script.
Early on in my career I had a creative director who used to look at a script I had written and say "nice language". For months I thought it was a compliment, until I realized it wasn't. It was the "faint praise" that damned my scripts. It's not about language.
Because I'm a writer, it took me a long time to stop thinking about words and start thinking visually. In fact one of my early TV spots for Hush Puppies shoes started with a simple idea: reward your feet for all they do for you by buying them comfortable shoes. I had the idea at home one night and wrote out the whole script in about five minutes on a sheet of canary typing paper --- but I couldn't think of a visual. The next morning I read it out loud to my art-director friend Marty and he knew exactly what to do: show a pair of bare feet going through the things the voice-over described. Without a great visual, the script would've ended up in the wastebasket. Instead it ended up winning us our first Addy awards, and went on to win more.
Once you've become accomplished at writing for television, it's hard to go back to print. TV is just so much fun. But actually your print ads get better because you've learned to think visually, and better understand the relationship between words and pictures.
Get the picture?