I first want to say that Grant Thornton is an amazing place to start or continue your career. The people are so great and the work creates extreme personal and professional growth.
I initially was given a referral and received a phone call from a recruiter at Grant Thornton. We had the phone interview then, and some questions along the line of "Tell me about a time when something unexpected happened and what you did?". Also was asked to describe a time when I worked in a team and there was friction. After that phone interview, I scheduled an on-site visit for about 2 weeks later.
The on-site visit was great. I interviewed with 2 different managers and was asked mainly why I want to work for Grant Thornton and why I want to get into consulting. I was also asked about what specific types of consulting I want to get into. I was taken out to lunch with 3 other employees and everything went well. After that interview, I was called about a week later and told that everyone really liked me, but there was no budget to bring me on at that time and I would be called back when something opened up.
About 3 months later I was called by the same recruiter to set up another on-site interview with 3 different managers. This office visit was also great. I was taken out to dinner the night before the interview with 2 associates, 1 manager, and 1 other person that was interviewing. The interview the next day was great. I met so many different employees and everyone is extremely personable. I interviewed with 3 different managers and was called the next business day with an offer.
My biggest advise is to understand your personal and professional goals and how they line up with Grant Thornton has to offer. Grant Thornton highly values its culture and the "fit" with an employee. Before my interviews, read a book on how to more effectively answer interview questions, how to ask better interview questions, and I came onto this website, took every question I could find, and made sure I had an answer for every one of them. I also knew my resume very well and was able to explain everything on it. Be sure you have questions to ask the person interviewing you. Try to customize them too and not have them be the very general questions like "can you describe a typical day". Most of all, be yourself and get to know the people you will be working with.