How do I effectively help someone with case prep?

I don't have a consulting background whatsoever but I've been giving my friend general guidance about the recruiting process as he's a STEM major with no knowledge of business internship processes. He recently got a case interview at Capital One and said their casing is more formulaic and rooted in math.

I'm going to case him in a few days, and was wondering if anyone could provide any advice as to how I can best give effective feedback and mock interview to the best of my abilities. Any insight would be appreciated, thanks!