And then smile some more. A somber face on television looks terrible. And on television, a small smile looks almost somber. So let out your natural enthusiasm with a bright smile. If you naturally talk with your hands and arms, keep on doing so.
Television likes things that move.
No matter how discourteous the interviewer may be to you, stay nice, and don't blow your cool. Remember, you're trying to make a good impression on the folks in television land, who may notice how you act much more than what you say. If you stay calm while the interviewer works himself into a hissy fit, you'll score points for the good guys. Being nice, by the way, doesn't mean you can't be assertive. You just have to be nice while doing it.