Stephanie
Listen to your heart. You'll probably know the moment you step on campus, or the moment you start reading something unexpected about your school. It's not a feeling you'll be able to describe.
Don't worry too much about money or what "ranking" the school has - most schools give scholarships, and it's okay if a school is right for you even if it's not "perfect" in the books.
Make friends! Don't lock yourself in your dorm room to study all night. After you graduate, you won't remember that test you aced - you'll remember staying up until four watching shooting stars on the quad with your friends.
Don't be afraid to talk with your professors outside of (or after) class. Most professors, during office hours, sit around hoping a student comes in to talk with them. If you have questions, ask them! Your professors care about their subject a LOT, and desperately want you to care about it too. That's why they're professors.
Start writing your papers before three AM the day they're due. ...I don't expect you to listen to that one. But try. :-)
Amanda
Visit a lot of schools and talk to the students to see what they have to say.
I
Choosing the right college is not about the name of the institution. It's about finding a school that meets your needs. If you learn best in a large lecture hall being taught by a TA, don't choose Illinois Wesleyan. If you want a school that values one-on-one relationships with students, faculty, staff, and administrators, this should probably be toward the top of your list.
Kelsey
I would determine what factors are most important to you and use them to decide what college is best for you. Also, make sure you go on college visits so you can see what the campus is like. Also, don't be shy about asking the college students questions like "What is the social life like?"
Melissa
The most important aspect, excluding doing the research about different majors, prices, and facilities, is to most definitely visit the campus! My advise is to visit more than once if you are seriously considering a particular school. Sometimes colleges and universities look really great on paper but they aren't what you expect when you get there. And trust me, it is a lot easier to send a letter telling the school that you have made different plans other than attending their institution, rather than spending a semester's time of money realizing that it is not the fit for you.