It is very important to have confidence when you face an interview. To gain confidence you should have knowledge of three aspects.
A. Knowledge of outer world:
1. Basic concepts: You should have a basic knowledge of the stream that you are into.
2. Depth of Knowledge: If your basics are strong then only you can have depth of the subject which is very important to prosper in your field.
3. General awareness: You are paid to solve the problems of the society, so it is very important to have general awareness in order to understand and solve their problems.
B. Knowledge of inner world: Inner world is all about you .Your strength, weakness, attitude and behavior.
1. Strength and weakness: You should be aware of your strength and weakness so as to apply your strength and take corrective measures to overcome weakness.
2. Skill set: You are hired because of your skill set which will be useful for any company to achieve their goals
The way you try to express the knowledge of both internal and external world to the people around you. It includes language, vocabulary, fluency and even body language is very important part of communication.
If you have all the above mentioned 3 skill sets then you will be able to gain confidence in an interview.