Mirrors is a well-known group activity that is great as a warm up. It gets kids working together and paying close attention to each other.
Music is extremely helpful while playing Mirrors. Have a variety available, including soft mood music, upbeat dance music, and music that will appeal to different emotions. The music will effect the types of movement the students come up with.
Have the students pair off. Each pair has an "A" and a "B." If there is an odd number of students, you may choose to participate. I have successfully had friends work in groups of three, with one student being the actor and two being the mirror at the same time.
A will be the actor and B will be the mirror. Start with slower music, and let the kids ease their way into this exercise. The two partners face each other, and B will mimic everything A does. Periodically, you will call out "freeze!" Then, when you call out "defrost!" B will become the actor and A will be the mirror. Do this a few times throughout the activity.
You will also change the music now and then throughout this drama game. If you have no way to do so smoothly (ie, you have to change a tape,) then you can call out "freeze" for music changes, or just do them as the kids move. Make sure everybody gets a chance to be both actor and mirror for all of your musical selections.
Statues takes Mirrors a step further. As a warm-up, statues develops cooperation and an important element of trust.
Again, the students should work in pairs when doing this activity for the first time. "B" is a lump of clay, and should stand and remain relaxed. "A" is the artist. A will mold B into different positions and shapes. When you tell them to, they will switch roles.
Statues can be a fun activity to perform in front of each other. Each pair takes a turn doing this in front of the group.
On a more advanced level, statues can be used in improvisation classes. Have two As mold two Bs on stage. Then, from whatever positions they start in, the Bs must improvise a short scene.
At its core, statues is a good drama activity to build trust among student actors and prepare them to work closely with their acting partners in scenes and on stage.