Along with regular visits to your high school guidance counselor, begin requesting college application packages early on in your high school stay. Build up a tentative list of colleges and universities you would like to attend, and request admissions packages from them. Familiarize yourself with the application process, and consider what a college application entails so you can plan accordingly. By looking over a few college application forms, you'll get a good idea of any high school coursework you may still need to take. You might also begin thinking about any extracurricular activities you may want to be add to your college applications to help make you more attractive to the admissions board.
I second the notion that the interview is as much for the student to get to know the school as it is for the school to know the student. While interviewing at Reed College, the admissions representative asked me what I types of things I like to read. I told him that lately I had been reading a lot on race and class in America. He then picked up his bike helmet from his desk and said to me, “Describe this blue bicycle helmet in terms of race and class in America.” From that simple request I learned what type of thinking would be ahead of me at Reed. And from my answer, the interviewer learned what type of thinking I would be able to lend to Reed.