For starters, don’t join in. Don’t try to make yourself fit in by excluding others.
Be a friend to someone who is being bullied. Urge them to tell someone who can help. Offer to go with them if they are reluctant.
Don’t question the person about why they are being bullied. It may make them defensive, thinking you’re blaming them or that they did something wrong.
If they refuse to report the bullying, do it yourself. You can keep your name confidential.
Don’t confront the bully in a way that could lead to a fight. You might get hurt.
Observe the behavior of the person being bullied, and watch for any harmful signs.