Know the companies You've got maybe five precious minutes to explain to the company exactly why they need you for their current needs. Use the materials provided by the career fair organizer to determine which companies have open positions in your field, then check them out. Company websites are excellent sources for details on current openings, company news and product information. Armed with this knowledge, you'll be able to describe your most relevant experience and skills to each interviewer, be able to ask insightful questions about the company, and identify which of their current openings you are most qualified for. They will appreciate your preparation.
Nobody wants to hire a sourpuss.
Keep in mind that the interviewers are people too, and a warm smile and sincere word will help to quickly establish a quality rapport. Your personality and communication skills are being evaluated as carefully as your skill set. The key here is to be assertive, but not aggressive. Ask how to get that critical second interview, and how to best explore the possibilities more. If a second interview isn't arranged on the spot, don't despair.