when you first start out you probably have a settler and a warrior, right?
make sure you toggle on the resources on map so you know what spot is good for a city. once you find a good spot to build a city you should start building a worker. and use your warrior to explore.
when the worker is done. use him to make improvements around your city. a lot of the players, myself included, automate workers right away. a worker for a city is good way to go.
once your first city reaches size around 6 or so you can consider building another settler and send him out to establish a 2nd city. the way the game flows, it doesn't really allow you enough time to build more than 4-5 cities before your territory touches other nations'.
you should also be mindful that what constructions you build in the city will best help you maximize your objective for the city, be it for food, production, or other stuff