A campus interview is a chance for the institution to present itself to students. Therefore, a campus interview is not only about sharing information about yourself. It is also an opportunity to learn about the college or university. This simple fact may put you more at ease.
To prepare, do some research about the university or college and try to see how you would fit in. What could you bring to the university or college? Also try to articulate to yourself what your goals and dreams are for the future. Universities and colleges like nothing better than when their graduates succeed in the world, advertising their alma mater in the process.