To best prepare to interview for a Summer Analyst position at Accenture, I would recommend that you prepare a set of stories/experiences when you've demonstrated certain skills Accenture is looking for and be ready to share that with your interviewer when they ask their questions. Accenture is looking for you to show them what you're capable of not just tell them! I would also spend some time reviewing cases and practicing them with a friend to best prepare you for the case interview!
I applied for an technology consulting position, so I did research on the tech consulting industry as well as the specific position I was interested. I realized that Accenture had strong focus on SAP, therefore I went into depth of learning the basic functionality of SAP and how the implementation impact on companies run their business. On top of that, I also went onto Accenture site to learn more about the company culture as well as current trend within the company. At last, Accenture is a consulting company after all, so case study is a must. I would recommend read through "Case in Point" to have a general understand of the module they use to solve business cases and also do some extra research on the technology implementation and its risk(because those are normally not covered).