Ask yourself, what motivate your character? Why are they the person they are? What incidents in their past have most-shaped who they are in your story? What are their dreams?
Once you have the answers consider how the events in the story will intersect with the journey your character has had until now. Will it change who they are? How does their personal history influence how they will respond to actions in your story’s plot.
By answering some of these questions, you will gain insight into your characters and how they will act and the journey they will take when they face all the challenges you as the writer will throw their way.
Grab a piece a paper and jot down a few things that have happened to your character in the past. Then, jot down some of the challenges they will need to face in your story. See how they will meet (or even fail to meet) those challenges.