The teacher's role in this process is that of a guide and a facilitator. There are many ways to have students select topics for writing. Have students select their own topics and develop them in a way that is suitable to their audience and purpose. Writing improves when there is an audience other than a teacher and a purpose other than a grade. Provide teacher directed prompts that still leave room for some student choice and do not deprive students of either ownership of their writing or opportunities to improve their writing ability.
Good writers think about what they are going to write and organize their ideas.
To do this they consider the purpose for their writing and the audience for whom they are writing. You can create an on-line story map and summit your story to the web. Read A Jury of Her Peers and learn about the elements of a good short story. Maintain a supportive environment that incorporates the multiple intelligences, provides rich resources, and gives ample drafting time in class. Respect the writer's ability to make choices about purpose, audience, form, content, and length and to refrain from setting artificial limits or constraints upon these areas.