Be prepared to give a full explanation of what might be only a single-line bullet item on the resume. Often there will be final questions related to some of the qualitative issues that resumes do not reflect. Make sure all your answers position you as the candidate that meets the company's needs. Ask for a business card and inquire as to the next step. The full interview usually takes place behind a curtain or screen at the employer's booth, or may be in another part of the hall altogether.
Most employers use the full interview only as a secondary interview.
In other words, you have to be invited to the interview based on the previous screening interview or mini-interview. Be prepared for 20 minutes or more, but probably no longer than 30 minutes, since most companies have a tight schedule to keep. Consider this interview the same as you would any full-length interview. Be aware that you may actually be interviewed by technical or line managers. You will be asked a great number of qualitative, open-ended questions and will be expected to provide elaboration of your answers.