You have your resume ready, you know the dates of the job fairs, but is that all you have to do?
Before you go, you should spend some time on your plan of attack. Most job fairs post in advance the names of the companies that will be in attendance. Review the list, see if any of the companies fall within your targeted area of expertise. Complete some background research on that company so that you are able to converse with the representative at the fair. Make sure that your resume reflects the skills you have that will best suit that company. If there happens to be more than one company at the fair that you will be focusing upon, prepare an individualized resume and cover letter for each of the companies. Don't just "spray and pray".
While you are at the Job Fair, make sure you have your "elevator speech" ready. You may only have a few moments of time with the recruiter and you want to make the most of them by being able to express why you would be a good fit for their company. If you are allowed time to ask questions, you could ask about opportunities, job responsibilities, and skills and/or past experience they are seeking. Also, you may want to ask about the application and hiring process and the appropriate method and timeframe for follow-up.
Do you ask for business cards from the recruiters? It is a good method to complete your follow-up (based on the follow-up timeframe) and send a thank you note or email. Use it to notate what you spoke with the recruiter about at the fair.
After the fair, make sure you send recruiters any additional items they requested. Send your thank-yous. Track everything in your log so that you can jog your memory when they call for the on-site interview.