Expand its empire
You have started the game and you own a city. That is good, that is an excellent start, but it is not enough: you wish to extend your influence. It is perfect, because you can colonize new cities. Your first city, the metropolis, has a special infrastructure that is not found in subsequent cities: the Capitol.
The Capitol allows you to have an additional city for each level you build. Once the level has been increased, simply open the window of operations and send a colonisation to a plain. Ideally, it is a good idea to optimise your location by choosing a field next to others that can be annexed: these grant production bonuses for certain resources. This means you can consider mining specialisations, or simply take advantage of them passively.