A slate is when you stand in front of the camera and say your name, age and show the camera your profile looks (either side of your head). Giving a clear slate is important so the casting director and person watching the tape later (ad agency executive, producer or director) knows who you are and how old you are. It also sets the stage for a good first impression. If they can't understand your name and age they may be leery about whether they'll be able to understand the name of the product coming out of your mouth.
Many commercial auditions involve nothing more than a slate and a couple personality questions. This is common when the role simply involves a person you see on camera for a second who has no lines. These personality questions are general, typically: "What do you like to do?" "What are your hobbies?" "What was the last movie you saw?" The best way to get a callback is to be engaging and show off your personality. Don't give a one-word answer. Elaborate and have fun with it. Also, never talk about acting, dancing or singing. Everyone in the business does, and it's uninteresting. Producers want to see real people, so open up and be yourself.
Be very aware of what you wear. For commercials you generally want to dress the part. However, if you notice in commercials and television in general, there are certain "no nos." Never wear clothing with big logos, pictures or wording on them, as it is distracting on camera. And if you're auditioning for a Nike commercial, wearing an Adidas shirt won't win you any points with the ad agency. Also avoid excessive stripes, dots and patterns. These don't look good on camera. Bold, bright colors are usually best. Avoid black and white. They absorb and reflect light on camera.
If you're supposed to pretend that you're talking to someone off camera or looking at someone off camera who isn't really there make sure you always choose the same eye line. In short, decide where and how tall the person is so that when you look at himyou're always following the same eye line. This makes your performance make sense to the viewer. Next, always start on your mark when you enter the room and give your slate. The "mark" is a piece of tape on the floor where you are to stand so you'll be in position for the camera. Some marks are "T" shaped, designating where your feet should be placed, while others are simply a strip of tape to give you a general idea of where you need to stand.
If you're supposed to deliver lines, they will be written on a large cue card (or white board) and set off to one side of the camera. If you don't have the copy memorized or forget your lines you'll need to reference this board. Shift your eyes to look at the board, grab a line and then look back to the camera to deliver it. Don't talk as you look at the board; always read the cue card then turn back to the camera to say the line so the camera catches you saying it directly to the viewer.