Completely agree with Guennael especially on use VC frameworks and enjoy the process!
To my experience as expert, what people are often forgetting is the following (put in very simple terms)
Consulting is about improving the clients situation. Therefore, you need to understand the situation of the given business. And at the very basic of every business is the question "How do you make money?"
Once this is really understood (and given it sounds so simple many people actually forget about it), the rest of the case becomes much easier... Then just be client-friendly and you ace it!
P.S.: Do understand many business types, regularly pick up business journals (WSJ, FT,...) and make your own cases!
P.S.2.: the question also includes "how do you add value?" :)