Incorporate writing prompts. Often, a prompt can spark an idea, which can turn into an entire short story or an even longer piece. Prompts can come in other forms besides the written form. For example, it is a good idea to make copies or multiple prints of an interesting picture to give to the writers. Many times no further instruction is needed other than to tell the writers to write what is evoked in them through the photo.
Work to build a creative environment. If the group of writers is working in one particular setting, think of inspirational quotes to put on the blackboard or hang on the walls. Also consider hanging artwork or interesting posters in the space. Playing music softly in the background can also help a writer's process while they build off of a prompt.
Encourage the writers to share their work. Ultimately this can be the most rewarding and engaging process of writing. With their narrative voice open to others, writers will be more conscious of their ideas, style and syntax. This sharing can take on the form of a formal workshop in which one writer's piece is discussed by the entire group while the writer remains silent, or it can be a less formal situation. The point is to get ideas from others and to provide helpful feedback. In any case, advise the group to "mark up" one another's work with tips, suggestions, questions and concerns.