thanx to all of you for giving your valuable suggestion.

Just relax and be yourself. You shouldn't worry to look dumber than your interviewer, because the other way around, YOU would be interviewing him. That's how companies usually work.

There are many things to remember when doing a face to face interview. Here are a few I practice with my students. 

-Make sure your apperance is neat and tidy. People DO judge on looks.

-No gum chewing!

-If you are physically with the person, posture is crucial. No slouching.

-If you have to shake hands, make sure you have a firm grip.

-Eye contact is very important.

-And like it was said above, confidence!

Good luck! 

confidence.