Because consultants work for a wide range of companies they are able to give you exposure. Therefore, when you go to an agency, present yourself as you want to be presented Have a clear CV outlining all your personal and educational details. The personnel consultant is paid by the company to look for the most qualified and most experienced person available.
Graduates are trainees for most positions, and companies are loath to pay agency fees for trainees.
However, it is equally true that when companies want to employ a graduate they are usually looking for a certain kind of person with a specific qualification. Phone and make an appointment first. Remember that if you are not replying to a specific job advertised by the agency, then you are a non-targeted candidate. A targeted candidate is one applying for a specific job advertised - obviously any intelligent consultant is going to spend time on targeted candidates first. BUT, if she is clued up, she is going to market your application every spare moment she has to clients who may well be able to use your qualifications.