I got 4 onsite (invited to the company) interviews and my first job through this type of conferences 7 years ago. Definitely suggest to wear formal suits (jacket and skirt). And don't pass any opportunity to talk with potential employees even that you think you are not ready yet. During the conference interview, stay positive and enthusiatic. Hiring managers look for experience AND personality (somebody who can fit into the team). So it would help a lot for the first job hunting if a student can show her pleasant personality.