You should always be over-prepared when going into an interview.
Besides having your work portfolio and extra copies of your resume on hand, you should also have copies of your certificates and work samples. These can give your interviewers an insight into your skill sets and professional experience, and add credence to your resume (which is essentially a sales spiel for your career).
A common mistake is to focus on a banal list of functions and responsibilities that you held in your last position. This doesn’t really tell the interviewer anything however- rather you should focus on your achievements and accomplishments, and the sort of positive contributions you can make to an organisation.
Interviews can be a nervy experience, but you should never panic.
Do not let your nerves get the best of you, but rather exude an air of confidence. Stay calm, pause and think before you answer. Avoid playing with your hair or tapping your feet incessantly. Put yourself in the shoes of the person conducting the interview. If you’re not confident selling your own skill set and personal attributes, that isn’t a great portend for you offering much value to the interviewer and the company.
It’s also important to remember that an interview is a two-way conversation. You should always appear interested and responsive, and take the opportunity to ‘interview’ the interviewer about the organisation, your expectations and career prospects. This shows that you are prepared and enthusiastic for the position, and will give you an edge over other candidates.