Get the person excited about it. The spokesperson must be enthusiastic, clear, concise, and well versed in the subject. TV news shows, especially the morning and news features have segments for guests. These are a valuable source and hosts are always looking for guests. A person's face is the focal point for the camera.
Hands are the second most important feature.
Don't be static, let hand movements accentuate words. Look at the interviewer and the other talk show guests. Don't slump or swivel in the chair and avoid fast movements. Sit up straight and relax. Speak clearly and consisely.