Never leave a sour first impression again during any type of interview. When you first meet someone who is influential, make sure you're dressed appropriately for the occasion. Give a handshake that exudes confidence. Speak eloquently and articulate clearly:
Speak clearly and at a moderate pace. Work on varying your voice intonation. You don't want to come off as a monotone bore. Also, speak the language of the person interviewing you. Avoid slang and jargon not associated with the job you're interviewing for. Use proper grammar and vocab[ulary]that reflects a higher education. If people can't understand you, it's hard for them to like you.
It is important to realise that during such events, the first impression can make or break your chances of promotion or appointment. Be yourself, but be a person you'll like too.