Every character comes from somewhere. Creating a family history and historical setting can add great depth to writing. Below I offer a number of exercises for creating relationships among characters in linked short stories or longer works.
Picture your characters. Having a physical picture of your characters can help you get to know them. Find a photo or a painting of your fictional family. At some antique stores you can find images of real people who lived in the 1920s, 1930s, etc. Or look through magazines or newspapers or search online for contemporary photos or paintings. Once you have your picture, put it at your side and write everything you observe in the image; this description may well become part of your finished work. Then, imagine what came before the picture was taken—and what will happen after the shutter snaps and the people move on with their lives.
Visit your characters at home. Families often have specific places that are important to them: the family home, the family farm, a vacation house, a wilderness area, a family business, a neighborhood, etc. A well-drawn setting often reveals a great deal about characters. Spend some time mentally visiting the places that are important to your characters, and write down everything you can. These descriptions may work their way into your piece. Also, by being able to picture clearly the spaces in which your characters move about and live their lives, you will have an easier time envisioning scenes and selecting details as you write.
Build a family tree. Draw your family tree. Include your protagonist's siblings, spouse, children, and parents, but also put down aunts and uncles, grandparents, great grandparents, etc. Write down full names and years of birth, marriage, and death. If some part of your character's lineage is unknown, leave it blank. Even a largely blank family tree can inform your writing; not knowing where you came from or who your ancestors are can be as significant as tracing your family history back to the Mayflower. You might think that Great Aunt Beatrice has nothing to do with your story; put her down anyway. The more you know, the richer your writing will be. A family tree can help you to avoid continuity errors. If Grandpa was born in 1926 in page one, the family tree can help you make sure that he's the right age on page fifteen.
Bury your characters. Imagine that your fictional family has purchased a cemetery plot that will hold twelve: two rows of six, one above the other. Draw out the plot and think about who will be buried where. Who is already buried there? For whom are the other spaces reserved? Who will be next to whom? Who gets the space under the oak? Who will not be buried in the family plot? Why? Think about the family politics underlying these choices. What kinds of monuments will the family choose to mark the individual graves? Imagine a scene taking place at the cemetery. Who is visiting the plot? Why? What happens?
Summarize your character's life. Imagine that one of your characters has just died. Think about how his life will be memorialized. Will there be a service? What will be said? Who will say it? How will the life be summarized by the living? What has he left undone? A newspaper obituary is another type of summation of life. Try writing your character's obituary. What were his accomplishments? Who are his survivors? This exercise will allow you to see your character's life as a whole and to explore the impact that it has on family members.
Put your characters in the world. Do some research on the historical periods in which your work is set. Make note of world events and major headlines. Even people who are concerned only with their own affairs live within the context of history. Learn about the politics, wars, technology, and fashion trends of the period. Integrate these into your writing. Great Aunt Beatrice may have churned her own butter wearing a gingham apron and written letters by hand, but your protagonist might shop for organic butter in her Birkenstocks while chatting on her cell phone. Every accurate historical detail that you present adds verisimilitude.
Remember that every character—even long-forgotten Great Aunt Beatrice—is the protagonist of her own life story. If you write with the belief that there is no such thing as a two-dimensional character, you will find your writing taking you in unexpected directions. You might discover that Great Aunt Beatrice actually does have an important story to tell. Doing these exercises may allow you to uncover some of these latent stories. If you are working on short stories, you can develop some of these unexplored glimmerings into complete stories in their own right—and thereby create linked stories. Even works that focus on a single character can benefit from this approach; every character, after all, comes from a specific time and place. To paraphrase John Donne, no man—or character—is an island.