Don't feed the microphone. After you've made your points, be quiet. It's the reporter's job to fill time or edit blank spaces. Insist, gently, that you be allowed to finish. Avoid ambush interviews.
Most people look like a deer caught in a car's headlights.
Ask the reporter to call for an interview. Don't talk over your shoulder as you walk away. When possible, develop rapport with the reporter and discuss the subject background. Always assume, however, that the tape is rolling and the microphones are recording you. When possible, select a background which you feel best illustrates your story.