First impressions are extremely crucial. You should greet your interviewer with a smile, firm handshake, eye contact and a pleasant demeanor.

-Remember your role.
Of course you certainly want to be friendly and comfortable, but be careful not to act overly friendly or too familiar. Abstain from using slang, foul language, or any terminology that might be considered inappropriate such as something sexist or in poor taste – even if your interviewer does!

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Body Language
If you hear something that concerns you during the interview do not convey your concern in any way to the interviewer (physically/body language or verbally). Bring it up in the debriefing and let us address it with the client on your behalf – it would be more effective given our relationship with the client and we may be able to negotiate matters more effectively.