It's very easy to get caught up in the interview preparation process without taking the time to look at what is actually involved in the syllabus. Good candidates at interview will have a knowledge of the Oxford PPE curriculum so make the effort to delve in to what you'll be studying - that way if the tutors ask you, you'll be able to talk confidently about what you're applying for.
There is the obvious benefit as well that you might realise the course isn't for you....!
