My son's rule: Direct frontal attack. Get in the bully's face in front of a crowd of other kids and challenge him to a fight. You'll probably lose, but nobody -- including the bully -- will ever take you on again. They'll go for the weaker ones who won't stand up for themselves.
Yeah, he got expelled for a few days. Once. After that, nobody bothered him again. Word was out, he'd fight.
Maybe not the best way, but it worked for him.
His little brother did the same a few years later. Though not as strong, and far more the easily-victimized type, that one time bought him a lot of respect and saved him from a lot of future bullying.
In an ideal world kids wouldn't have to deal with such things because the parents would raise their children to be kinder, nicer people. In an ideal world teachers and principals would care about bullied kids and put a stop to it.
We don't live in that world.
SusanHere