Fidgeting
Excessive sweat
Long periods of silence.

These are some of the signs of nervousness often displayed during interview sessions. In my years of conducting interviews, I have noticed this as a major problem sometimes acting as the defining factor between offering or denying a candidate the position.
Yes we all know how intimidating some interview can be. However no matter how qualified you may be, the employers want to see how confident and convincing you are. Because let's face it, you will need some level of confidence in carrying whatever role you are assigned. So you need to project your self confidence during the interview to show the interviewer(s) you are the right candidate for the job.
Often, people under estimate how important it is to exhume confidence during interviews. But I can tell you it is extremely important.
So just how then do you do this?
Here are a few tips to help you deal with the anxious moments and boost your confidence during interviews.

RELAX. Find what helps you relax before big moments. Some people turn to music. Others to motivational speeches. Identify what works for you and apply it.

LEARN TO LISTEN. Cultivate the habit of listening through before attempting to answer. What this does is it gives you time to compose yourself and also think through your answers.

BE ENTHUSIASTIC. Employers only want to hire people who are enthusiastic about working for them. Your chance to show that is at least to speak enthusiastically. Even if you have the right answers to the interview questions speaking in low tones devoid of any passion does not help in projecting you as confident.

USE RIGHT BODY LANGUAGE. If you have ever done any background work on interviews you would have found out that employers take a close look at the candidate's body language as much as all other aspects of the interview.
Wear appropriate clothes. If there is something wrong with your clothes, you will soon find out as all eyes will be on you albeit for the wrong reason. And this is bound to affect your confidence.
Sit appropriately. Not slouched.
Make eye contact when you speak.
Do not fidget.

LIVE FOR THE MOMENT. No matter what happened before the interview, leave it outside the door. Do not bring any baggage with you. Even if you sat in the most horrible traffic en route the interview, act like nothing happened. However if you suffered an unfortunate incident before the interview, try and contact the employer beforehand to intimate them of the situation.

DO YOUR HOMEWORK. One thing that is bound to knock your confidence is being embarrassed openly and nothing can be more embarrassing than not having done your homework prior to the interview ( i.e making sure you know your CV) because employers can ask questions based on what is on your CV and if you can't answer this it can be very embarrassing. Infact I can tell you that from that moment, the interview just goes downhill.
Also spend time researching the company. It is very embarrassing not to know anything about the company you want to work for.
Lastly practice interview techniques. If need be ask your friends to help in a mock interview session.
Leave no stone unturned to achieve success.

http://saotheemploymentcoach..co.uk/2013/06/you-need-confidence-to-succeed-at.html

Thanks for this eye opener.am highly enlightened.

Self confidence is very important when during an interview because you future employer want to know if you would be able to do the job. Your level of confidence would be able to determine your capability. That's why good preparation is the key to self confidence. If you don't read for an exam, how do you expect to pass... So you have to do your homework 12 things to do when preparing for an interview