It's a bit vague.
I think the key points are
- get 2 outposts in Neolithic, and 15+ tribes. If there are lots of mammoths to hunt (20 inf each) you may want to linger even longer (edited)
- 2 adjacent on the best territories (prioritise rivers and early FI expansion)
- 3rd outpost should be forward placement towards nearest neighbour / good resources / horse /copper. You want 1 of horse or copper to be in one of your claimed territories or next door - but wait until ancient before placing the outpost because it costs 20 if adjacent to your city territories, instead of 60 (edited).
- go to ancient and found capital, and immediately attach the adjacent territory. Settle scouts if needed to max out your industry pops and enough food for positive growth (but nothing else - settled pops eat more than they produce!) Growth comes from buildings at this stage, not from working farmers.
- found the 2nd city as soon as you have enough influence. Then keep claiming and attaching territories as you can
- build pottery workshop in both cities, then food and industry buildings
- 3rd city ideally by taking over an independent (to save influence)
- being 1 over the city cap is ideal (10 inf cost and cities generate much more than that)
- claim any nearby territory that has good tiles and key resources
- attach territories to the nearest city as you can (enough influence and 100% stability)
- don't worry about attaching the perfect territories to each city, you can detach and adjust later. Attach the closest if possible as it's cheaper.
- ignore civics unless they are immediately useful. 50% off founding outposts is useful, then switch to 20% off attaching
- in practice most of my cities are captured from indys or neighbours so you can't always choose placement and have to adapt to what you're given. Assimilating comes a lot later but you can swap territories around in late Medieval after you've finished expanding
- beeline +1 city cap techs if you see an opportunity to add a city, or go Persia in Classical if you have too many opportunities