In my world building, I strive to create a complete community and culture. One point I address is what the various characters do. There are butchers, bakers, and candlestick makers, and every other vocation and avocation needed to make a vibrant society.
For my characters — primary, secondary, and background — I explore their lives from birth to death. I learn their joys and sorrows, successes and failures. I meet their family and friends. I learn about their interests, skills, and talents. I discover their suspicions and biases. I experience the adventures on which they go.
Even though this information may never be revealed in the story, knowing their lives allows me to know how each character reacts in various situations. This brings more depth and consistency to the story, and more importantly, it provides a wealth of background and future ground that can lead to new situations or to foreshadowing in the current story, and even to new stories.
Characters make the story. Invest in them and they will reward you.