In his excellent book on writing, "The 3 A.M. Epiphany," Brian Kiteley suggests an exercise called "Body English" in which group members write about a conversation that takes place with no words. Kiteley recommends that it might be easiest to write from the point of view of an observer watching two people. (Ref 2) Write only about their movements, gestures and positions. Read your writing to the group and discuss in specifics how it conveys meaning through action.
For this exercise each group member should bring two or three items to the meeting --- a sparkly piece of jewelry, an old book, a stuffed animal, any common item. Put the items in a box and ask everyone to reach in and draw one out. Then write for 15 minutes describing the item you chose without using adjectives or adverbs. This will force you to use active verbs in your descriptions and make your writing more lively and vivid.
In "Writing Fiction," Janet Burroway, author and writing instructor, offers this group-oriented adaptation of John Gardner's exercise, "The Barn." Mentioning neither the circumstances nor any specific emotion, write for five minutes describing a barn as seen by an old person whose son has just been killed in a war. Share your work with the group and pick out words and images that convey the emotion. (Ref 1) This exercise develops your ability to show point of view by seeing things as your character would.
If your writing group meets in a public place, pick out an individual and write for 15 minutes on five things that will happen when he or she leaves. You can use this exercise to focus on plot development, making the incidents that happen build on each other, and to examine action minutely. Decide as a group what in particular you'd like to focus on, or just throw the exercise out there and see what your group members do with it. Share your work when you're finished and discuss any issues or possible plots that appear.