Kindly, remove your hat. And your puffy ski jacket. And your gloves. Yes, it is freezing outside. But this job fair is an indoor event. There is a coat check near the door. If you're worried about theft, carry your coat over your arm. Clunky, but preferable. I once worked with someone who kept his coat on all day in order to take frequent smoke breaks. You don't want anyone to think you're that guy.
Plan ahead, so you will know which companies will be attending the job fair. Check out the job openings posted online (Indeed.com is a good place to start) to find out which companies are hiring for your skillset. A successful networker, my friend Yael told me she does some internet stalking prior to events so she will know who to "bump into" when it counts.
Plan ahead, so you will know what to say when you meet people from your target companies. Yael admits to investing enough time in advance so that she knows something unique about those people she wants to bump into. At a job fair, you have two choices. You can say, "I'll do anything! Tell me about your company!" Or, you can say, "I'm really good at this one thing and I saw a posting that fit my skills; can you tell me who I should talk to about that?"
When someone approaches my table at a job fair, and they look friendly and ready to work, that's a great start. When they tell me exactly what they want to do and which of my job openings they like, I want to jump up and down and schedule interviews on the spot. Be that person. And remember to put that hat back on when you leave. It's freezing outside.