You're doing yourself a disservice if you march into a college fair and refuse to look at colleges outside your preconceived, often arbitrary, criteria. You may always have pictured yourself at a well-known school with a huge student body in a major city, and that's fine. But that shouldn't stop you from considering other options. Listen to what the representative says and complete an information card. Don't limit yourself to looking only at schools that your friends and classmates know. Expanding your options has no downside, but you'll miss out by limiting your choices too early in the process.
All schools post admissions statistics, location and student body size on the College Board website (see Resources). Don't waste your time, or the representatives', by asking questions you could look up online later that day. Even if you're unfamiliar with the school, grab a brochure but still ask the representatives questions. Some questions to which you cannot find the answers online include "What are some unique features about your college?" and "What factors do students attending your college find most appealing?"
Each table will have information request cards that add you to a school's mailing list. Each information card typically requires your name, high school, email and postal addresses, and majors of interest. Print a spreadsheet of mailing stickers, each containing the necessary information, and take it with you to the fair. When you want to receive more information from a school, all you need to do is place a sticker on the information card rather than writing it by hand at dozens of tables.
Just because you already visited a school doesn't mean you can't stop by and say hello. If the representative works in the admissions office, he may be the one reading your application so think of some thoughtful, specific questions before attending the fair. Even if you know a lot about the school, tell the representative that you were reading up on the college and were particularly excited by a certain feature, such as the psychology program or study-abroad opportunities.