How do you make theme music?

on average I write 20 pieces of music a month, all of them one minute long, for music beds for commercials. The way I like t to work is, I play the video part with no sound and then write the music in REAL TIME to what I am seeing on the screen.. It's seldom I have to do it over. Usually I do at least 3 pieces of music for each commercial then upload them all to the customer and let him/her make the final choice.