There's just no other way to impact your students than to model what you want to see in them. In any work environment there are social groups and in many ways cliques. If you want your students, especially the girls, to stay away from girls' cliques that are mean and engage in positive, inclusive behaviors then you must do it too.
Students notice everything you do both in the classroom and during your time 'off' around the school. They know if you're gossiping, leaving out another staff member, or generally engaging in your own clique type behaviors. Don't do it!
While at school, even on breaks, remain an educator who subscribes to the highest standards of behavior. Be inclusive, accepting, nurturing, and true to yourself. There's just no better way to teach your students to be strong and true to themselves than to do it yourself - no matter how challenging it may be.
Look for opportunities to include others, walk to your own beat, and be yourself. In other words don't just talk the talk, walk the walk. Your students will spot your phoniness a mile away and your lesson in acceptance and positive behaviors will be worthless.