1) Definately wear a suit.
2) Make sure that your ready to answer questions relating to airlaw, navigational techniques, instructional techniques, etc.
3) Be prepared to give a short brief on any of the intial exercises (Ex 4-13).
4) Make sure that if your asked to fly the sortie that you briefed that the brief and the flight match up. It may sound silly, but the chaps at Oxford like to do things correctly.
5) Be prepared to say "yes" a lot when asked questions like: "would you be prepared to go the extra mile for the student/ company".
Good luck.