The key to a successful interview is in thorough preparation. Finding out as much as you can about the position, the company and the industry will place you in a strong position and give you the necessary confidence to handle most situations. Similarly, a careful analysis of your own career history will allow you to highlight the most positive aspects of your application and prepare you for in-depth questioning on any weaker points.
You are being interviewed because the employer needs to hire someone and wants to find out if you are the right person for the post. Through interaction which takes place during the interview, the employer will be evaluating your strengths and weaknesses, your qualifications, skills and intellectual qualities. As well as assessing your technical expertise, your interviewer will probably delve deeply to determine your attitudes, aptitudes, stability, motivation and maturity.