Educate
If we teach people what bullying really does to people and we explain what bullying is we can cut down on bullying. How many people are going to bully someone if they realize they may be indirectly killing that person. The answer is not many.
Start groups for victims of bullying
If we give the victims of bullying a place to openly vent so they don't bottle up their emotions we can help lower the number of people who commit suicide or acts of violence. Starting a group isn't hard or time consuming but it brings people together and giving them the potential to make new friends and improve their self-esteem.
Be friendly to everyone
We don't have to be everyone's friend, but if we see someone we don't like we don't have to insult them. We can walk past and say hello or even offer suggestions on how they can improve themselves in a positive way. As long as we avoid insulting people or excluding people we can help them stay happy with themselves and maybe find that we really do like those people after all.
Apologize
No one is perfect and everyone at some point says something that can be considered offensive. When that happens instead of walking away you can just apologize and make sure they realize you didn't mean to hurt them, especially if you did.