Remember that there is no right or wrong solution to the case. Most of the time you will be given a case that is an old project the consultant worked on so he/she will be the only one knowing what was done and they know that you will not come up with the same answer that took them 6 months to find...
Be smart, think about your structure and analysis, ask question, think out loud, calculate, estimate, ask questions, ask questions. They are seeking to find out how you reason, how logical you are and what your capabilities are in terms of synthesizing and seeking solutions. As I said , there are no right or wrong solutions but your approach and structure of the case solution is of extreme importance. Here's a proposed approach: 1. Clarify case problematics - do you understand the entire problematics? If not, ask questions. When you understand, synthesize the situation before continuing 2. Outline required information to perform your analysis; think here of possible sources, if none available how you can estimate and if still not possible you guess but be clear in explaining how you came about with the guess (remember: Structure and analysis) 3. Outline your analysis approach and provide details of how you would advance the work, resources required. 4. Formulate possible solutionS (note plural - joke; How does a consultant answer the question - is it possible? A: It depends!) 5. Finally synthesize your conclusion and what could possibly be next steps in the process.
As an associate you will not be managing teams but in some instances resources such as BA and SBA. This will not be a major part of your interview. Consultants are managed not as much by formal leadership as they are by thought leadership and this is what they will seek to identify in you. They will expect you to think "out of the box" and be creative in solution generation as you will not only analyse but also draw conclusions from and sythesize reports. Because you do not have a consulting background it is even more important that you show your capacity as both a generalist and specialist but more important is your capacity to structure, synthesize and propose solution.
Stay cool, clear, sharp and be the best you can be - good luck