This is my shitty method. Just take a point in history. I took the end of the bronze age, early cities, people working out iron, etc. Find the societies you'll be working with, get your concept of them, try to avoid things like 'greek citystate-but INDIAN'. Try for things like 'fishing-based society, excellent galleys, large deposits of silver nearby, equatorial climate, on the continent, near large archipelago extending out into the ocean'. So, ocean-dependent society. They have supplies of precious metal. They desire naval superiority to their closest neighbours, so they raid primitive tribes on remote islands for galley slaves. Once you have the basics for a half-dozen societies, imagine what might happen over a century.
100 years later, they have a standard silver currency, probably a centralized leadership, greatly inflated population, hegemony over several nearby smaller cities, and probably trading links with one of the other nearby major societies. They might end up with similarities to the greek citystate, but after 15 'turns' of worldbuilding, there can be interesting permutations.
I did this with a bizzare conglomerate continent with a fertile area the size of west africa, three seperate archipelagoes on the north east corner and an Andean mountain range along the northern 'spine' of the continent. I ended up with a Middle-Kingdom-esque empire with constant internal strife containing an area the size of the Amazon, collections of minor states with common-defense pacts in three places on the continent, a group of regularly replaced despots ruling the dirt patches the big players didnt want to conquer, thousands of tribes of cannibal Zen tribals living in the alps, and a HRE-esque decentralized mess in the northern archipelagos.
Any conflicts or bits i was unsure about, i just rolled a d% to decide, e.g. 'how heavy are taxes on foreigners', with 100 being severe and 0 being laissez faire.