Wear dark color suits with white or light color shirt (gentlemen need tie).

Practice questions and anwsers with friends.

If you are not too comfortable with your oral English, prepare your research or work in handouts and make copies for the interviewers. Try to pay attention to the interviewers and answer their questions. Ask them questions related to the company, the position or themselves.

When I was looking for my first job, I did not get an offer until my 3rd or 4th onsite interview. (But I did get good practice from the first few interviews.)  After that I always get offer if I choose to go to interview. So practice, practice and practice with your friends.

Good luck.