Go back to when your character was much younger. Preferably when they were a child, a teenager or in their early twenties taking the first steps in life as an adult. Write a scene about something that happened to them that shaped them to who they are now. It could be a tragic event, a great loss or something beautiful, like a birthday party in the garden on a hot summer’s day.
A great way to get to know your character even better and give them a fuller, more all-round personality is to know where they came from. What shaped them to become who they are now?
After this you can fast forward to the future and imagine them as a very old person. Let this person write a long letter to their younger self. It will be the last letter they will ever send.