People only try to bring others down if they, themselves are not happy. I tell my daughter to feel lucky that she's happy enough that she doesn't feel the need to bully. That any person who bullies is much less happy than she is and there's no need to pull them further down. If you are bullied (verbally); keep your head up. Say to the bully, 'I'm sorry you feel that way' and walk away. Know that they are only bullying to try and make themselves feel better, deep down they don't want you to feel bad; they just don't know how to deal with their own pain. Don't be angry at them; sympathise.
If it's physical, then it should be dealt with by an adult. If the victim is an adult it should be dealt with by the police.