To be honest there is literally nothing you can do to prepare for the case study in advance-just make sure you have some business sense in you and thats what they are looking for because since candidates from all backgrounds apply so they dont expect you to have a MBA mind but they do want you to have some business like approach and knowledge. As long as you have those, You would be completely fine. The case study is relatively easy-I would say the easiest one I have faced yet. I applied for the Audit service line. As of the competency part, they have stopped doing the usual of give me an example of this and that time. Instead they present you with four big competency style questions and ask you to choose one amongst them and talk it through in detail. I can remember two which were "a project/hobby/assessment etc which you have found most challenging" or "An achievement you are really proud of". The good thing is that you can literally talk through anything. Luckily I had one in mind which kind of covered both-I talked about my passion to the learn the piano. The difficult bit is that they want you to go into proper details like what lead to the passion, what did you do beforehand, any critisism or challenges you faced, how did you overcome them, how you kept yourself motivated, why do you think you are so proud of it, if you were to do it the second how would you approach it differently etc etc etc. One more advice I would give is that for the usual questions of why deloitte why Risk, actually write down your answers and learn them by heart like a test that way you wont be stuck during the interview. Retrospectively it was no where near as daunting and nervous as I had anticipated it to be. Just be professional, have a business sense, think about your competencies and just remain calm as if you belong there(a little cliche but it works).