Here is an easy format to use for fiction book summaries. It is generic enough that it can be used for multiple genres. The format focuses students in on character traits (C), plot outline (A), setting (S), and personal response (T).
I use this outline to structure my monthly independent reading assignments. Students keep the instruction sheet with their independent reading book and use that as a bookmark/note sheet to help write the summary.
The rubric I use to grade the assignment is included. It reflects that requirements that my building has for independent reading responses. I've kept the file as a Word Doc so that it is easy to edit to customize for your school/grade level.