At a college fair, you will win bonus points by dressing up a bit (suits not necessary, but something other than jeans a plus) and actually talking to the reps instead of standing by while your mom picks up a brochure and forcing it to you to fill out. The rep at a college fair is likely to be the same rep who reads your application. So start making a good impression immediately by asking good questions and being polite! Ask for their card before you leave in case you have any other questions later.
As for a tour, call the admissions office to see if you can stay overnight or tour your specific major's department or sit in on a class... anything you can do to get a real feel for the campus is great. The more you do, the better you'll know if you're a good match or not!