Thanks in advance.
In your interview talk about how much you want to represent the school, be an example to the younger kids, and give back to the school ect. Throw in a few of your ground breaking schemes on how your going to change the school, but in reality, teachers are far too busy, to really be able to implement them! They sound good in your interview though.
Sit up straight, look the interviewer in the eye while speaking, smile alot, think about your awnsers!
Good luck, I have really enjoyed my time as Head Student, it's something you can always be happy about. Who could forget the personal statement sweg too, that comes with it too!