Step One: Themes and Threats
Decide as a group what the themes and threats for your city are. Both of these are some kind of problem. A theme is a problem that is a constant for that city, has been around for a long time, and permeates the culture enough that it can't be tied to just individuals or specific organizations. Threats are recently created problems, short term with potential to become long term, and are typically tied directly to specific individuals and organizations.
Step Two: The Faces of Themes and Threats
This is where the group makes up the people that best represent these themes and threats. These faces will start to give you an idea of what factions are important for the city.
Step Three: Status Quo and in the Know
Using your themes and threats, figure out what the current balance of power for the city is. Who wants to keep people safe, who wants to make sure things don't change, who wants to shake things up? Then you figure out how much these factions know about the supernatural. You can add more stuff to this later on as the group comes up with more ideas
Step Four: Locations
Brainstorm locations for the city, come up with a cool sounding aspect to show why they are important, and give them an NPC face.
Step Five: Review
Review what you already have, and fill in any blanks you still have.
