When you speak, purposely slow down your speech because all of us have a tendency to speak fast in front of a camera. Television is much better when one enunciates and speaks slowly and clearly. An interview is not a commercial and you can seem insincere if you look directly at the camera. If you have ever watched Nightline when there are several people in a conversation at the same time, you will notice that each of the respondents are looking right at the camera. When I started giving interviews on television, I also noticed that I had a tendency to use my hands a great deal.
Hand signals can be effective if kept within a small area.
Keeping your hand motions to within this area can allow you to make your point without being a distraction. If it is a call-in talk show. Follow the rules above. The radio feed is an opportunity to get exactly what you need to get across heard by the radio station's listeners. Pretty much, no matter what question they ask you will answer the question by including the main point and theme that you want to get across.