Don't forget a business card so you can follow up with the recruiter later. Jot down on the back some notes about your conversation. Show your interest . Give a firm handshake and smile with eye contact. That's a great first impression that shows confidence.
Nothing is more boring than a one-sided conversation.
Send a thank you note. To make a real impression, send it soon after the fair to the companies that most piqued your interest. Don't wait for companies to call - call them first. Set up informational interviews or a company tour. Bring a little box of mints with you.