Walk up in there with a suit on, most importantly.
Calmly walk up to the podium. Make sure your tie is straight, and the say with enthusiasm,
"YO YO YO MOTHAFUCKAAAAZ, I'm bout to be yo bitchin' new prez. And when I am we bout to change some shit in here. I'm talkin' use of cellphones, chewin' gum, more bathroom breaks and if you sleepin' the teacher cant wake yo ass up"
"Homework? Mannnnnn we got shit to do today. Don't even bother doin' that shit"
If you can get all of that out before you get in trouble I promise everyone will love you forever.
But in all seriousness, take polls and shit like that at lunch and find out what people want. Focus on changing things and getting better funding for clubs and finding ways to introduce new field trips and shit.