I go to a school where people get bullied often and many people get in fights, and I get bullied often and I (almost) always get them to back off.
so here are my tips
1. probably the most important, be intimidating, what I mean by that is that you never want to act like they have a possible chance at winning, because they don't.
2. that brings us to number two, be confident, a lot like the first one, when you are confident, you know what you are saying, and with enough confidence, they know what you are saying.
3.defend yourself. If someone hurts you, fight back, there is no possible way to get in trouble for self defense. But never, ever swing first. that is not self defense. if they punch you, you tackle em, never the other way around. That is just a way to get in trouble. the best part about this method, is that, when done right, they wont come back for more.