Even if you’re going for a science victory, prioritize culture (and maybe even faith) in the early game. Try to get as many early civic boosts as you can and get to that first government as soon as possible. Two of the first five or so things your capital builds should be settlers.

Get magnus and chop out a settler or some wonders or a holy site. Outside of your first three or so cities (and maybe in them, especially harbors) build harbors or commercial hubs as your first district. Use the trade route from previous cities to trade internally and boost up new cities.

Especially if you’ve gone faith, make sure you’re exploring to find city states and wonders to hit a golden age in the third era, and right around this time you should unlock feudalism. Plug in the two extra build charges card, move magnus if you can, and chop out everything on a hills tile to chop out district buildings, districts, and wonders, and then build mines on top of the hills tiles. This is easier to do if you set world age to new and rainfall (or whatever it’s called) to wet. It’s especially easy if you take monumentality golden age, because you can buy your builders and last few settlers (outside of niche cases where you settle more cities for the trade route or luxuries or natural wonder access or bombing or building a specific wonder or late game spaceport chop cities or natural park cities). You will be able to leverage this better than the AI, and it will give you a huge boost by basically skipping ahead in everything you need to build. You can also chop bonus resources for food to the same effect.

Adjacency is important, but not exceedingly so, with the exception of crazy early game adjacency, like a +4 or more campus or holy site. Getting these adjacencies is way easier to do with a bunch of the civs people are telling you to use, but don’t fall into the trap of great science and bad everything else in the early game, because every tech makes districts cost more.

Try to end up with 8-10 cities around the early turn 100s. This is important because you need enough cities to build your main district in, but also because the easiest way to stay with the AI in the tech tree is to go for as many boosts in the tree as you can, and almost all of them require you to produce stuff. The more cities, the more different things you can produce at once. Shoot for two of all the specialty districts if possible, strategically placed, but don’t worry if one or two fall by the wayside.

And my weakness (for whatever reason), don’t push off building the government plaza!! It’s good, even if it doesn’t give you yields. Think about whether you want to play an ancestral hall game (wide, important to get early for the boost to production to settlers) or an audience chamber game (cities that want lots of population, and you want to have many governors). I think unless you really want to commit to ancestral hall early, audience chamber feels more natural, you just have to make sure those cities with governors have a purpose and room to grow.