Register for the event as soon as you can. This will increase your exposure on the website to students planning to attend the event.
Be early and stay till the end. Some job seekers have many obligations and cannot get to the fair until the very end. Staying to accomodate them may lead your organization to finding just the right candidate.
Staff your table appropriately throughout the day.
Bring plenty of business cards and materials to distribute. Students enjoy connecting with a person and not just the organization's name.
Dress professionally, but comfortably.
Get the most out of the day by making yourself as approachable, engaging, enthusiastic, and friendly as possible.