Write a script. Even though a commercial is only 30 seconds long, you still need to have a clear story with a beginning, middle and end. You should think about what message you're trying to communicate and tool your script to fit that objective. While you're writing your script, be careful to note the technical requirements you might need to shoot the commercial. Avoid costly effects, copyrighted music and images or locations that you cannot access legally. You'll be glad you avoided the hassle of these issues when/if your commercial makes it to air.
Storyboard the script. Storyboards are used to plot out and plan each individual shot needed in your script. In each storyboard panel, include the type of shot, either a close up or 2:1, two people in one shot; whether it's a long shot or a wide shot; special effects and in what direction the actors will be moving. Storyboards are a lot like a panel comic strip, they show the action and dialogue of the story shot-to-shot.
Cast your actors and recruit your crew. You will want to make sure you have enough people to help you shoot your commercial. If you have the budget to rent lighting and sound equipment, you should find people who know how to operate those elements for the shoot. If you're not great with the camera and wish to be the director only, you'll need to find a steady-handed camera operator. And, of course, you'll want actors; contact your community theater, local high school drama department or university theater program to find actors who are willing to help you for free to get resume credit and experience.
Secure permits to shoot in any public areas before you begin shooting to avoid costly delays.
Shoot your commercial. Take time to make sure you get multiple versions of each shot so that you have options when you're in the editing room
Edit your commercial and add music. There are many different computer programs you can use to edit film and video. Check out your local university's film department to see if they have a facility you can either use or rent to do your post production work. If they don't, you may need to buy a software package such as Final Cut Pro, iMovie, Adobe After Effects or another similar program. Check out the Internet and check in with your geek friends, as they might have a suggestion of freeware or shareware that you can download for free.
Publish your commercial to DVD or VHS. Once you're satisfied with your rough cut, lay down the commercial onto a video medium and deliver to your local television stations for air-play.