Get lots of copies of your resume ready to go.
Plan well which booths you will visit, so your time doesn't run out. I'm sure you won't want to spend the whole afternoon jumping from employer to employer. Don't limit yourself to just booths that fit your interests. Look for generics (but relevant) or alternatives.
Be sincere! When you sit to talk with one of the recruiters, they know you are nervous, and they don't expect you to have a huge resume. If they wanted more experience, they wouldn't be at a job fair.
Try learning a bit of each company you plan to visit, such as their competitors, products, philosophies and what are some of their company policies. Use that to your advantage. This is the most important part, you must know the ins and outs of a company or you'll never get an interview.
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Don't go for jobs with bad people. Seriously there is a reason why a company is looking when turnover of staff is high. Heaven help you if you walk into that job.