I'd say the most macro thing to realize going up to Emperor is that Civ 6 rewards chasing your victory very narrowly. There's no sense trying to create a diverse and robust empire that can do anything decently well, limited tiles, district slots, and long production times means that you should decide how you're going to win early on (minimum first 100 turns) and gear all your play towards that. The AI for example, hyper focuses science, so if you're not doing that, you won't beat them barring bankruptcy (less so on Emperor than Deity obviously, but same principle applies).
Do you have a lot of mountains around your start? This makes for great Campuses, plus strong early defense, and since Mountains often mean Hills as well, solid production. You're lucky you might even find some Geothermals. Therefore, this is a probably a good science game. Plot out your early campuses first (somewhere between two and four), and make cities around that. Once you're in a more stable position you can expand beyond your cradle, you probably want to end up with at least 8 cities, although you can easily get away with as few as six on Emperor if they're of good quality.
People have discussed monumentality, but if you're not in a position to get good faith, finding a heavily forested city to put your Governor Plaza +Ancestral Hall with Provision Magnus will do the job nearly as well. It will take some time to set up, don't be afraid to "waste" a few chops getting the hall online, the sooner your start this next wave of expanson the better, even if the last couple cities end up lagging a bit. It helps to improve tiles underneath the forests while you're doing it, but this requires more builder charges.
Spawn next to Desert or Tundra? As others have said, terrain-adjacency + Work Ethic is basically free on Emperor. At that difficulty, you probably still want to HS first district, but you don't have to Prayers or otherwise hyper-cripple your expansion most of the time to get religion, just watch the Great Prophet Meter and Religions screen. Remember that first Religion will probably go to Stonehenge (should never be you, it's possible on Emperor, but awful), and the last WILL go to Arabia if they're in the game, so always try to get at least second-to-last to be safe. This strat can lead to....anything, production's the top yield.
Side note about Tundra: Means many more barbs, alter opener appropriately.
Lots of flatland/low production? These are often the hardest starts, but remember that chopping is your friend. This often means lots of room to expand or an early war. If it's the former, Culture Victory's on the table, you have time and room to sculpt your land. Not something I'd necessarily recommend to new players, it's the most complicated way to win, but it's satisfying to learn. What's good about culture is your early game doesn't matter too much as long as you have the land to scale well late. If you have a close neighbor and low-production, find a defensive spot, prep for war. This is either a great Dom or Science game, if you win the early war, you'll either have a highly promoted kill squad, or a lot of land to Campus up.
Coastal? This usually means war or culture. Coast does give appeal, but it also corners your expansion for a while. Remember the AI doesn't do naval combat, if you have enough boats to kill the city, you can do so with no resistance. You're gonna want boats, because Barbarian galleys are obnoxious, if you have no navy they can destroy a coastal expo before it does anything, and even Archers do very little. Barbarian Quadriremes are a straight up, "do not enter this coastline without Men-at-Arms" sign that you should heed. This can be extremely annoying if it's shielding a camp that spawns other annoying horsehocky, but it is what is. The only way to stop them is 2-3 boats plus a land attack, and even then you're probably taking risks, not to mention a lot of production. You might decide to simply not improve sea resources until late, but traders prefer water routes, so ignoring aquatic barbs really limits you.
Now, I just realized you posted again, so I'm gonna respond to some things there, because advice tailor to the player is always better.
I use a combination of religious faith (I always found a religion, and take the Voidsinger Secret Society for those +4 faith Obelisks) and trade routes (Harbor + Lighthouse is almost always my first builds in new cities)
Voidsingers is generally the best Society (I didn't consider you'd be using the Game Modes actually, which ones if you don't mind sharing) imo, although if you have an early war opportunity, Vampires can be amazing. They're even great at peace because of castles. The specified builds are obviously for coastal cities, and yes Harbor should usually be first District in those, but if they don't have Fresh Water, granary is sooooo important. Being capped to three pop is really bad for production, even four is kind of low with improvements granting some housing, if you get that granary housing+food, it'll speed everything up over the medium term. Not only are granaries super cheap (they can even be directly bought if you can afford it) but Harbor doesn't give anything but a few gold until the Lighthouse is up, which doesn't directly help the city at all. Plus, districts increase in cost as you do research, so Harbor first can be a very long first build. Sure, a coastal city needs its Harbor ASAP, but a city's first build should be made with its weak status in mind, it wants immediate results to start being better, so it can contribute SOMETHING faster. Also, don't neglect the Reyna and Moshka promotions that let you buy districts. They're probably not something you'll get until quite late (often during a third, almost colonial phase of expansion), but they're super strong. Monuments are always good as well, but less necessary to build first past the first wave.
On maps with a lot of coast, I can win domination fairly easily with most top civs, and even a few less powerful ones, by going after the Venetian Arsenal. The AIs never build it, in my experience. I also always get the Mahabhoti Temple, same reason.
So you noticed how bad the AI is with naval, good. Not much advice here, but I'll point out the pattern here with these two wonders: The AI does not city plan, so any Wonder that has somewhat complex requirements tends to get neglected by them. Other examples include the Mausoleum, Colosseum (two amazing wonders to try and grab btw), Colossus, Terracotta Army, Zimbabwe, Ruhr, etc. Really most wonders that have to be put next to a specific district, although there are some Wonders they prioritize anyway, Forbidden City and Alhambra off the top of my head. Also, Panama Canal is always free, but always a meme.
I choose the 25% bonus production on districts for cities without a district, and as I said, new cities after the initial 5 or 6 is almost always Walls, then Harbor, and buy an Obelisk.
Ooooooh, idk about this one chief. That Pantheon is actually pretty bad. If you do the math, 25% isn't actually a lot of total production before the city has its first district, although if you build that district for a lot of turns it can add up I suppose. The thing is, you probably don't want to be building one thing for 30 turns anyway (why Wonders are so situational, that's a lot of time before realizing any return). If you want production, the one that gives production and faith on strategic tends to scale really well throughout the game, as its value increases as you uncover more strategic. The trickle of faith is less valuable with Voidsingers, but still okay. God of the Sea is also really strong if you have the tiles for it, turning great food and good tiles into decent or at least okay production tiles lets cities grow quickly while building decently. The terrain-adjacency plus Work Ethic combo mentioned is amazing, but it's a bit of a slower burn, doesn't become amazing until scripture (policy card that doubles Holy Site adjacency). If you want to do a Science game, Divine Spark is actually really good, it lets you compete for the strong early game Scientists, and helps you propel through the later ones faster, although many are less impactful.
I abuse Magnus, of course, especially the no population loss when building a settler. In fact, that is often my 2nd pick instead of another Governor. If Im lucky enough to get a Golden Age, I choose "buy civilian units with Faith" and expand like made with the faith Ive saved up (I barely use enough for missionaries to convert my own cities)
Good, this is often correct. If you did terrain-Work Ethic, converting can be worth it, but abusing Monumentality is super strong. That said, Medieval Monumentality expansion is still quite strong, especially on Emperor. Even just using it to purchase a bunch of Builders is amazing, improvements are so important. You should be able to afford it, assuming you get Government Plaza up by Political Philosophy, you have three Titles to play with. Four if you then get Ancestral Hall afterwards, but don't feel like it's necessary to delay expansion until then if you have Monumentality.
I could probably make the jump to Immortal and win with Simon or Hojo or Jaoa on a mostly water map, but Domination is, again, the only viable route.
Possibly, the AI can't handle Archipelago well at all, but you have to keep in mind yourself that Barbarians are going to be way more annoying on those maps. Also if you do spawn on an island with an AI on that difficulty....things can get hairy real quick. That said, although it's really boring, I cannot imagine you're incapable of winning a Religious Victory. Maximize faith, pay attention to when Apostles have debaters, and you'll be fine.
