A most under-rated behavioural trait that most interviewees fail to display during any interview is enthusiasm.
Most interviewees seem to under-estimate the importance of showing that they are really interested in getting the job. Therefore during interviews, they seem to be either indifferent or lackadaisical. No serious employer can warm up to an apathetic interviewee. Most assuredly, all employers expect interviewees to show appropriate levels of eagerness, interest, sincerity and courtesy during the interview, and be honest in putting forward these qualities. Above all, try to be as natural as possible!