I would simply introduce yourself, tell about who you are, why you think this position is so important, why you are so excited to have the opportunity to be the school president... and then begin to talk about your goals, what you want to do in order to make the school better, maybe how you are open-minded and ready to hear what the students want, etc. Talk about the things that you know the students are pushing for, and your take on them, how you plan to lead the students to get what they want. Good luck.