what kind of job it is?
Confidence is the key my friend. Dosen't matter if you are applying at McDonalds or Microsoft. If you want to be successful in profesional world then you have to gain your confidence level. One way to increase is that you have to BELEIVE IN YOURSELF....when you are going for your interview, just keep saying this to yourself "I am better then all of those other job candidates".
When you meet your employer....Shake his hand strongly, of course dress sharp....compliment the person right away...could be anything...try to make them smile but not make them laugh....this is not an audition for comedy club but on the other hand, everyone like a person with good sense of humor.
Don't act over smart...jitnaa savaal pocha jaye utnaa jawaab....don't talk too much either...let them do the talking....and look into the person eyes directly when you are answering...even if its a GIRL!!!
Hope this help and good luck on your interview.