Confidence has been mentioned before as though it should be easy to acquire. Everybody is confident about their abilities in some activity or other. If I asked you to tell me something that you felt confident about, it could be cookery, playing sport or a hobby. If you analyse why you are confident at that particular activity, what would you attribute it to? Are you confident because it is a familiar task; because you have been told that you are good at it; because you are well prepared; or because you have studied how to do it?
Often, all these reasons apply, and that is why practising your interview technique is so valuable. Half the terror of an impending interview is because you do not know what to expect. Rehearsing in advance means that you will feel reassured about which questions may come up, and about your ability to answer them.
Increase your confidence by preparing thoroughly, packing carefully any items you might need if you are going to give a presentation, eg hand-outs or flip-chart pens.