Think before you talk. Don't be so eager for the interview that you launch into an explanation without gathering your thoughts together. It is ok to pause before answering. If you're being taped, they'll edit it out. Even if they don't, a slight pause doesn't look bad.
Most people talk too quickly on air.
A pause will help you speak more slowly. If the reporter asked a good question, say so. If being interviewed for TV, know in advance what you're going to do with your hands. If you brought props or charts, don't play with them. If seated, rest your hands on the desk or keep them below the desk out of site.