One strategy is understanding our sphere of control. There are some things we can (and should) control, such as our habits of being polite. There are others things that we cannot (and should not try to) control, such as the weather, especially living in New England where all four seasons can pass through in twenty-four hours.
This concept is helpful in dealing with peer relationships. We cannot control what others think, say, or do. If behaviors "crosses the line", of course we have policies and protocols for addressing issues of bullying. However, we cannot control "typical" negative behaviors of other people. Sometimes, peers are going to be unkind, or gossip, or be moody. While our caring teachers attend to such social-emotional dynamics by helping our peers to gain insight into their behaviors and cultivating the desire to change, it is often resilient-building for us to understand what we can do to minimize the negative impact.
We can control whose opinions we listen to and value. In our discussions, the students and I often talk about if someone is not a reliable and good friend, why do we care so much about what they think of us. We can choose to listen to those who are kind to us all or most of the time. We can take an inventory of who our trusted friends are and invest our energies in those relationships.

This short piece on HuffPost by Renee Jain: Teach your Child this Crucial Life Lesson (Challenge #2: Sphere of Control) is a short and helpful read.