In my experience as a newspaper reporter, the best quotes came outside the boundaries of the “formal” interview. Always on the record, sources were more relaxed and able to provide good material while waiting for the PR assistant to show up, or walking to the elevator when the interview was over.
The same goes for a technique we call the “awkward silence.” You’ve answered a question, the reporter looks down at his or her notepad, but the next question doesn’t appear to be coming. Seconds feel like days, so you decide to break the silence. That’s when you’ll likely go off track and make a statement that doesn’t quite fit the plans for the story.
If you answered the question, you answered the question. No need to dilute it just to fill space, so practice recognizing and dealing with that tactic. Better to stumble in your conference room during a private media training session vs. when the cameras are rolling.