You should be smiling 10 feet before you shake their hand. Act like this is the big one. If it helps you relax, feel free to remind yourself that this is just step one, but don't get so comfortable and casual that you lose your energy. Dress the part. No matter what type of job fair you are attending, or for what kinds of jobs, dressing for success is crucial.
Any employer wants to feel confident that they employ professional people.
This is your opportunity to display your understanding of professionalism. Finally, sell it. You have just a few minutes to make them want to place your resume in the callback pile. The job fair has become a staple of the job hunter's diet. If you use this tool wisely and effectively, you can get excellent results.