Much writing comes from yearning. Yearning is the intense feeling of longing for something or someone. Often it is related to something or someone lost or separated from but not always. It can simply be the idea of something or someone.
We all yearn for something. I yearn for freedom and to be immersed in nature. If all people yearn for something, your characters should too. In a love story characters might yearn for one another. Dr Zhivago is a case in point. What do you yearn for? What do your characters yearn for?