The first day of interviews consisted of two interviews from managers and directors of the firm. The first one was very nerve wrecking and lasted for over an hour. The interview did not consist of knowledge/education awareness questions. They have already pre-screened individuals per your resume and transcript to identify individuals academically qualified. If you get to the first round, it is to see if you can talk using manners, and with a smile. Tip: smile a lot, laugh when appropriate, wear business professional (black/gray suit with a white shirt/non-colored, tie that isn't Hawaiian, POLISH your shoes). The interview is challenging because the questions and discussions have absolutely nothing to do with the field of work.
If you make it through this interview process, you will be invited to an evening social event after which you will be introduced to your entire future prospective team. They will ALL be assessing you to see if your personality will be a good fit for the team. You will be taken out to dinner where again, the employees will outnumber the interviewees. This is again, to test your demeanor. Keep it professional, use humor, understand that these people are all human beings and want to see if they can stand working 80 hours a week with you during the busy season.
The day after the evening social comes the real interviews. You will be given a morning presentation. After that, you will have a series of appointments for interviews (4 or 5.) Each interview will last approximately 30 - 45 minutes. You will go to lunch this day with a few employees, and a few interviewees. There should be a 1:1 ratio over lunch.
All interviews are one on one. They are tough. They will ask you questions that pertain to your ability to handle clients in a professional manner, while delivering the quality standards that are expected to you. Be prepared. Know what your field does, and be prepared to answer what-if scenarios pertaining to client situations. Be prepared to talk to a partner during these interviews. This is the hardest day. Any interviewer has the right to object to your hiring. This is for good reason. Understand that it is part of the process, and they are in need of you.
They need good people and if you made the office visit, you already academically qualify. Just be yourself, stay relaxed, don't regurgitate rehearsed answers, stop and think for a few seconds before delivering a well reasoned response. Do these things and you should get a call within a few days from the Partner who interviewed you offering you a position. Don't ask about salaries, it will come in time.
I have been through harder interviews, so just remember that they are interested in you as much as you are in them. Stay yourself and shine!
Good Luck!