This is a great question. I have a couple of ideas on making a good impression at a career fair or association meeting. Research the companies that will be in attendance (choose 3 or 4 to really focus in on). Check out what cool things are happening either with their company or in their market. Bring these things up in your conversation, ask questions around them; this shows that you've gone the extra mile and that you are someone who is interested in their line of work. Ask them if it's OK for you to connect with them via LinkedIn and when you do, be sure to send them a quick note. Feel free to follow up with them and see if there are any career opportunities that you'd be a fit for. Thanks!