I think its great that you're thinking ahead. Keep that mentality moving forward and I'm sure you'll do great things in life!
The College Interview is a great way for you to learn more about the college and ask any questions you may have about the institution. Also, it gives the college an opportunity to get to know you and your interests when it comes to their institution. To prepare I would advise you to go over some practice questions with a friend or family member. (i.e. Tell me about yourself? Why are you interested in attending this institution? What are your academic strengths and weaknesses?) You'll find questions about the College Interview Process all over the internet for more example questions.
I would also recommend that you come with your own questions about the college. They may be interviewing you, but you should also be interviewing them as your college of choice. Be yourself and do not be nervous (easier said than done at times). Dress nice so that they see you are serious about your attending of their school and I am sure you will have a great interviewing experience.