I was on both sides of the coin growing up - Often the bullied but sometimes getting my chance to be the asshole kid.

It wasn't until high school when a kid was insulting one of my friends that really turned it. The kid decided, because I "stuck my nose in their business" that he wanted to fight me. The fight was one-sided because I didn't want to fight but the result was me getting myself into boxing and wrestling. Most people didn't know I had gotten fight training but people largely left me alone after that simply because I didn't back down or go passive anymore. It's not worth it for a bully to go after someone who could hurt them when they have so many targets who won't bother or don't know how to defend themselves.

I'd say, my best advice, learn how to protect yourself. Having the confidence to stand in-front of a bully and let them know that you won't take their shit anymore is often enough to deter them. Should they choose to "fuck around and find out", defend yourself. Try not to embarrass them, especially if you are in the US, but showing them that not only can you defend yourself but can fight, they are more likely to leave you alone in the future.

Before I got fight training I suffered multiple trips to the hospital for stitches and concussions. Afterwards, I never had to defend myself. Violence is not a great answer but when faced with violence, we must know how to and be willing to protect ourselves.