We are not solitary figures. From the day of our birth until the day we die, we belong to one kind of group or another. Family comes first, and in many cases, last.
School, which occupies many years, depending upon how far we go. While at school, we might join the choir, learn to play an instrument as part of an orchestra, or be a part of an athletic team, all in elementary and middle school.

Once in high school, our options blossom. We can act, advocate, dance, collect and motivate. We can play chess or video games, cheer for our teams, and act out a court of law. We can debate hot issues, build and compete with rockets and robots, save the planet and work in the science labs as docents.

Even if we don’t join an organized group, we are still part of a family of students. We have our cliques, no matter the name, to which we cling for support and encouragement.

Beyond high school, we spread out our options. There are junior colleges, four-year colleges, trade schools, and specialty institutions of learning. Once there, we are again presented with a variety of group choices.

My point is that we tend to congregate with those who share a common interest.
Your characters must also be a part of something bigger in order to be complex beings.

When you develop your characters, think about what they might like to do. Perhaps they join a mystery readers book club, participate in Zumba classes or work with scouting groups. Maybe they volunteer at a local food kitchen, build houses for the homeless, or repair benches at an inner-city church.

Your task is to make a list of those things that interest your character. From that list choose a few that you can work into a story. Be careful, though. Too few groups and your character falls flat. Too many and your character is overwhelmed. Unless, of course, that is what you want to happen.

Put on your thinking caps. Remember that each character is unique and so has interests that are different from other characters. There may be some overlap. For example, maybe they come together once a month to play poker, but the rest of the time they pursue their individual interests.

Good luck!