Be thorough with your essays. Align whatever you say about yourselves with what you have written in your essays.
Regarding case studies, I don't think you need to worry too much. It was pretty straight forward. 30 mins are enough for you to crack it. Read it once, then read it again. Go through each question one by one. Write the answers down in the way you'd want to tell them to the interviewer, if that helps you.
Most importantly, clear your mind. I didn't read anything on my interview day. Relax, the interviewers are quite sweet.
All the best!