Regarding television, film production, or for that matter any job working in commercials, the first thing you'll need is a job. “The most important part of being a director is having a job.” That's attributed to Eric Von Stroheim, who probably never shot any commercials.
The second thing to know is that while getting the first job is very important, getting the second job from the same client is the moment of truth. It's particularly gratifying if they're nice to work with, need to make a lot of commercials for a long time, pay a lot of money, and you get to be the one who makes them.
There are three phases to film or video commercial production or, for that matter, to production of any kind.