Firstly , if one on part interview is based on knowledge on the other hand it is based on our personality  appearance. So along with having good knowledge about the subject be careful of your appearance, your body language . Interviewers should feel that you are out f tension. Feel free , be confident of your self and try to speak truth ... you know the answer say yes or else no... most importantly do not pretend. Be free... comfortable ... show a little bit of hand movement for freeness . Goodluck!