I applied online fall of last year and was just about to give up on this. Then one day late January, I got a phone call asking if I was still interested. I said yes and scheduled a first round interview.
First Round -- short 20-25 minute phone interview, mostly talked about my resume and my interest in Accenture. I would definitely recommend looking at the Accenture website, learn about the core values and the different areas of consulting Accenture offers. A day or two later, I got a call to schedule a second round interview.
Second Round -- 45 minute phone interview, mostly behavioral questions "tell me about a time..." I was on GlassDoor reading about all the interview experiences. I was asked about leadership, teamwork, project work, etc. They really go into depth on the questions, asking several followup questions. I would recommend doing more research on Accenture, looking at example behavioral questions online, and really know your experiences. I practiced all my "stories" several times, made notes before hand so I wouldn't miss anything. Also, make a list of questions to ask the recruiter. I found a website with some questions and adapted those. I received a call about 1 week later to schedule an onsite interview.
Third Round -- about a month after the Second Round, I was flown the night before with the other candidates. There were about 20+ people in my session (morning) and 20+ in the afternoon session. There were 2 separate 45 minute interviews, 1 with a manager, 1 with a senior executive. They were more informal and conversational. I talked about my experiences again, although about half of the time were dedicated to questions I have. I had a list of 25+ questions, although we only got through about half. Following the two interviews, there was a 2 hour period for lunch, presentation, and questions. There were 5 analysts/consultants in the room and each talked about some of his/her projects and experiences. This was the time to ask about living in the area and such. I was flown back in the afternoon.
A day later, I received a call from my recruiter extending an offer. I was told the formal offer will be coming shortly.