Espe-
To answer your question: First of all, spaniards seem to have a pet peeve for people who wear socks with sandals, they say only americans do it, I donīt know if thatīs so, but thatīs what they say. Also, shorts are not big here unless youīre at the beach. In fact, I have never seen anyone walking around the street in shorts here unless they were an american or some sort of weirdo. Other than that I would recommend that your students be respectful. Thatīs probably the most important thing. Donīt go about shouting loudly and generally making a raucous. Try to speak to people in Spanish even if it sounds funny, and PLEASE tell your girl students not to try to hook up with every guy who yells "guapa" or "rubia" at them. They think weīre all sluts. It will depend a lot on where in Spain you go.
em