First of all, you should compile your resume in the most effective manner stating your qualification, skills and experience of your specific field of interest.
Make sure you have included the details of research projects that you have completed during your academics which will earn you an extra advantage over other people.
Try to get information about the companies that will be hiring people at job fair. Try to identify if there is any company relevant to your field of interest.
You should take enough resumes with you which will help you to apply to all potential employers of different companies which are related in your field of specialisation.
Dressing is the most important aspect as it created a huge impact on potential employers. They will judge you even before having a look on your resume. So, make sure you are dressed up like you are going for a job interview.
You should be fully prepared as most of the times, the potential employers conduct at the spot interviews and hire people who successfully respond to whatever they ask.