I have hired over 400 people in my days as a "businessman."
A few of the qualities all of my "hirees" had:
1) Self-confidence (or at least the appearance of it)
2) Good Attitude--a smile and open personality
3) Quick wit
4) Good dress(neat not stylish)
5) Well-groomed
Make sure your resume has no spelling errors. Get the names of the persons you talk to; and make sure they remember yours. Be agressive but not pushy. DO NOT ask them how much the job pays, that is a sure killer. You should have the attitude of "what can I do for you" not "what can you do for me?"
The most important thing I can stress is that you have to follow up on the initial interview. Contact the company, by phone, within a day of the job fair, and ask for a second interview--the first interview happens right there at the fair.
Read the "Knock 'Em Dead" series of books, particulary the one on interviewing, before you go to your second interview. My first boss at this company asked me questions directly from the Knock 'em Dead book on interviews. And I had the perfect answers, since I had read the same book the night before!