Listen to the questions carefully. If the reporter is working from the wrong premise, has incorrect facts or doesn't understand the subject, correct the misinformation first, then answer the question. Television is a special case. Think of concise, catchy ways to explain your point. Short answers reduce the chances of your quotes being taken out of context.
TV cameras see everything.
Wear nice clothing but not more formal than what you usually wear. Don't wear stripes or bright colors. Keep your arms at your sides if you're standing and in your lap if you're sitting.