I have generally played on noble, large continents or terra maps.
I usually start by trying to build 3 to 5 cities and enough units to defend them and any resources. By then then most of the good spots are taken, so my next phase is to identify cities that would be easy to capture and defend and that provide something I need (such as a seaport, gold/gems, iron, etc.). This leads to a period of war in which I build up to about 8 to 10 cities, then I try to stabilize everything with courthouses/markets and focus on specializing my city production, research, and upgrading my military. At about the time that muskets/grenadiers/cannon appear, I have another cycle of war to claim any other resources that I have found that I will want, to cripple an emerging powerful neighbor, or to finish off a very weak civ that has one or 2 remaining good cities. I wind up with about 15 cities, and by this time I am starting to prepare for the space race. In the process of the space race I will usually go to war at least once more to knock out the most likely competitor. Here I am not focusing on capturing and keeping cities, just on razing them, so I may not end up gaining many cities. If I am playing on a terra map, I end up founding a few cities in the end or capturing them for barbarians to gain things like uranium or aluminum, and I might finish with 20 cities.