Imagine you have an identical twin somewhere in the world, and that you were separated at birth. You’ve never met him and had no idea of his or her existence until now. (If you prefer, give this twin to one of your fictional characters.) Explore this twin and what his life might have been like. How might he be similar? How might he be different?
As a plot this might be cliche and trite (if fun), but it can make an interesting exercise nonetheless. It pushes you to explore the “what ifs” of yourself (or your characters). What if you’d been raised by different parents? What if you’d been raised in a different country? What if you had a different career, different friends, a different family path? And what would happen when you reunited?