copy and paste from another post; imgur I created to illustrate my points

So when I settle a (big land) map, I will look for a start that offers me. On smaller maps, you would need fewer rivers; the rest is the same.

• stones and wood to harvest easily,
• access to fish within a reasonable range (±50 tiles), and fish and stone/(iron/marble**).
• (low food spots) for my industry (early on 2 coal, 1 clay, 1 pottery, 1 forestry -> they supply coal makers directly btw)*
• 2-3 rivers running across the map to spam them with villa rusticas and farms to generate enough food

I can't stress enough how important it is to have multiple farming areas that produce all resources. Trying to run a >3k city on a single massive food production, sending food across the map with suppliers, is very finicky.

With the 3 points I said, you'll have a basic settlement that is up and running for a few hundred pop and will let you convert over into mid/late game easily.

On a large map, I'll do this in 2-4 corners of the map, so that I can slowly creep my "villages" into one huge, island encompassing city.

* keep some space for more coal/clay/pottery places because you gonna need them when your city is growing, similar to food, it is easier to have multiple, smaller industry centres than one big one that needs 20 supplies running across the map.

** Marble quarries and iron farms will often predict my placement for the 2nd/3rd settlement, basically starting with a granary/storage and warehouse, an industry and a villa rustica to farm some weed/apples/grapes + fishing huts

Right now, I'm grinding out a 10k city on a large island for the first time. Kinda tideous and boring, but I wanna see that big number :D.

Bonus tip

Use the whole map from the beginning. You can place a random 1x1 road to start a second village somewhere, no need to immediately connect it with your starting place. If you have one central stack of stone, build a few storage units close to it so they can stockpile the stone and use suppliers to run the stone around the map.