DON'T forget the French maid's outfit with the transparent blouse and bagpipes.... it worked for me!
Seriously, apart from mugging up on what you've been advised to probably the most important thing is to keep a cool head. If they ask straight questions THINK for a few seconds before answering - don't rush in with the first thing which enters your head. If you don't know the answer don't waffle, just tell them you don't know. If they enter into a discussion then put forward your personal views on the matter honestly and don't be overawed by the situation.
I wish you all the luck in the world and let us know how you get on.