I think the best advice would be to make sure you know your personal statement inside out and back to front cos they use it for 99.9% of the interview. My RVC interview was my first interview too and it was scary as hell as I didnt know what to expect. They are really nice tho and usually ask you a couple of questions about hobbies etc to relax you and ease you into it. Like Lucyrobyn said, dont try to make things up, if you dont know an answer, say you dont know. They wont mind, you're not expected to know everything! If possible, if you get asked a question about something you dont know, explain you dont know but have a go at the answer anyway. Even if its completely wrong at least they can see you tried. Also make sure you know your view about things like stem cell research / bird flu vaccines / vegetarianism etc etc as they like throwing in ethical questions. Good luck!