It reduces to the candidate being well prepared and confident. These are really the basic components of any candidate who 'interviews well'. The employer will also be looking to fill a post which has a particular job specification - in other words personal aspects besides the experience and qualifications that can be put down on paper. The interviewer will set out to ascertain that the candidate has these personal qualities, skills and abilities the company requires. These two essential ingredients are interlinked.
Good preparation instills confidence.
So the basic approach to an interview is to be well prepared. This means two things - preparing yourself practically for the interview, and gathering knowledge and information you can draw on during the interview. The worst nightmare for an interviewee is rushing around at last minute, arriving late hot and bothered for an interview. This shakes the confidence. Your mind is not on the interview, and your personal presentation will have suffered.