You need to do lot of paper work before you go in for your interview. So, it would be wise to reach the venue one/two hours before your scheduled time and relax for few minutes just brfore the interview

You need to wear proper dress (dark coloured trousers with belt and white or light coloured plain shirt with matching tie)

Nobody expects that you know everything. So, if you have no idea about a question, politely admit the fact and make an intelligent guess if you are asked to do so.

Never unduly critisize anybody or anything. Always support your positon with data.

If you are asked to take a stand on some real-life situation (you want to marry a girl from another community and your parents are opposed, so will you respect your parents' opinion or will you save the honour of the girl who defied her parents to come with you?) pause for a few seconds and take a stand be frim. Board will try to shift your stand by playing sentimental cards, but stick to your stand by reasoning out. If you change stand, board will assume that your are prone to manipulation and hence a liability to the government.