Talk to the interviewer, or in a panel situation, to the person you mean to address. Eye contact is important. Darting glances come off as untrustworthy. If you can't look at a person, pick something to focus on. If you are passionate about your message, just tell it and try to convince the person talking with you.
Gestures are fine for emphasis.
Don't be threatening, however. Finally, the message . You must be passionate and you must be truthful. You must not have more than three points to make. If you get an unexpected question, don't answer right away.