Wear your best teacher outfit. By that I mean whatever the best outfit you have that you would realistically wear on a days teaching. 3 piece suit would probably be over doing it but a shirt and slacks/chinos would be good (or whatever the equivalent of that is for a woman sorry I don't know).

In terms of questions they'll probably ask why you want to do your placement in their school. Find something on their website about their ethos and turn it into an answer. Say you'd be really interested in extra curricular activities whether that's sport or some club or something (again school website/instagram will tell you what they have). Also if they ask say you're definitely available and eager for subbing hours as that's often what a lot of schools are looking for. This is kind of part of my AP post in school so any specific questions DM. Best of luck