One of the hardest pieces of advice to give people is on how to present themselves at job interviews if they have low confidence and self-esteem issues. The problem lies in the fact that there is no right or wrong way to do this, no "one size fits all" companies approach. It does depend on the company culture and how they do things.
If possible do a brief research on the company. Try to find pictures on the internet. Are the employees wearing casual clothes or only suits? This can give you a hint at whether they are strict formalists or more relaxed, so you can adjust your approach. Can you find any online reviews or comments about the company? For example, we all know these days that Google has an image of a relaxed, easy-going company, while banks are very uptight.
Why is this important? Well companies that are more relaxed tend to be less judgmental, so you should relax and just be honest and be yourself. In fact, they might even be OK if you tell the interviewer upfront that you are slightly nervous. They might relax you with a friendly comment or joke and you will remove the tension from yourself.
On the other hand, if they are more uptight, they might not look favorable upon your nervousness. One thing you can do is practice a speech in front of a mirror. Practice saying your C.V. out loud, give a brief speech on your previous experience and achievements, but train yourself to do it with poise, a calm voice, and relaxed breathing. Look the interviewer straight in the eyes (or your eyes in the mirror). Train this until you can do it relaxed and with confidence.
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