Characters need to have strong personalities driven by passions and beliefs that are challenged to create the conflict of the story. The events of the time help to create the characters, but they must be strong and interesting enough to stand alone in spite of historical details. Certain elements of writing remain the same no matter what time period you set your novel. The story must be told through solide, strong and multi-faceted characters. The theme needs to be timeless and relevant to readers.
Every work meeds to be married to the theme.
Once you have made the decision about the historical period of your story it is time to begin the research. Start with reading popular historical fiction. Study the writer's styles. Read, read, read. Used under License.