Determine how large the city is, in terms of both population and geographic area. For example, if it's a large city, choose whether it is built upward, like New York City, or outward, like Los Angeles.
Decide where the city fits into the overall scheme of things in the state, nation or world. Your city may be in a setting similar to ancient Rome, the hub of activity for the known world or it may be on the periphery. If your city is set in modern America or a similar setting it could be a state capital or a rural town dozens of miles from the next city.
Sketch significant social elements of your city, including social class or caste, the significance of religion, family structure and civic organizations or social groups.
Create significant figures for your city. Depending on your work's plot, this might include city leaders, politicians, police or other authorities, business owners, criminals or any other sorts of people you'd like to create. In addition, you should create a profile of the average citizen in the city.
Add any additional details to your city you feel might be especially appropriate or compatible with your setting.