Winning Civilization VI on deity difficulty is a feat in itself. Deity difficulty makes it so the AI receives huge bonuses and therefore is way more aggressive than you might be used to. Civilization VI's huge player base makes it so winning on Deity is only the first step to become an expert. Here we will teach you how to face this challenge. This is a complete step by step guide on how to win on deity difficulty in Civilization VI.
First thing is knowing what we are dealing with in order to play accordingly. We are going to compare against Prince difficulty, which is neutral in terms of bonuses.
The AI not only has settled 3 cities when you're struggling with the first one, but it will also have 5 Warriors and therefore -knowing of its military might- will be very aggressive. Expect war early in the game.
Granted you don't rage quit or get wiped out in the first 20 turns, you will have to face a humongous disadvantage in terms of Science, Culture, Faith, Gold and Production all throughout the game. To compensate you will need more cities than your opponents or be very clever with districts and civics bonuses.
It is not necessary that you choose your victory path immediately, but know that it will depend largely on the leader you choose.
Domination and science victory are the easiest to achieve while playing on any difficulty and deity is not the exception. Although any type of victory is achievable, the most likely is that you are going to wage war and conquer some cities first, and only then, after having an empire capable enough, you will be able to pursue your chosen type of victory.
Newer and even experienced players can find it difficult to achieve a religious victory on deity. Building Holly sites early and getting a prophet is hard when you should be spending your production on expanding and defending your cities.
Newer players trying their hand against Deity AI are recommended to play an aggressive early game civ such as Scythia, Greece, Rome, Mongolia and so on. This is the most straightforward path because the early game AI is likely to declare war on you anyways.
Producing a granary, monument or workers before having an army might be tempting, but it is simply too risky as you might get wiped out by barbarians and other civs. The safest thing -and best- you can do is to produce Slingers, which will be useful to explore and clear barbarian camps. Focus on army/scouting (max 1 scout, slingers are prefered) first, then 1 or 2 settlers and finally city buildings. A good build order would be: Scout > Builder > Slinger > Slinger > Settler. Try and get the Archery technology as soon as possible.
Once you've explored enough you should get your warriors and slingers/archers back to home, war is coming and you want your empire (1 or 2 cities) protected from a brainless swarm of AI units. Put your army in advantageous positions. Archer/slinger on city and the rest in tiles next to a river to make it so the AI receives a penalty for crossing it. Your small army should be way more valuable than the AI's, if you play it right none of your units should be killed while defending (attacking is another story).
Unless you are really going for a religious victory there is no need to invest your production to get a prophet. If you do so you will have hardships defending against the AI humongous economic and military early advantage.
Depending on agendas the AI's are ready to go at each other's throats, once you receive a declaration of war you can ask another AI to join you. It usually costs only 1 gold to get a war buddy. This coupled with your good defense will make the enemy civ beg for a peace treatment, which you will only accept if you can't capture its cities and also the deal is good (all the AI's gold for 30 turns).
Advanced players adapt really well to the map and surrounding Civilizations, they know if and when the AI will declare war on them. Sometimes you get a lucky start where you have enough room to expand and at the same time the Civilizations near you are friendly due to their agendas. For instance, Gilgamesh's (Sumeria) leader agenda makes him easy to declare friendship with him, if his secret agenda (which is random) also favours you, then you will be safe from an early declaration of war from him. If you are in this very rare case of no early war declarations you must expand and build cities with powerful district bonuses (Campuses surrounded by mountains or aqueduct-industrial zone technique).
If you played early war well then you will have an experienced army and at least 4 cities to produce more units. Use the 50% melee/ranged production civic in order to spam archers (or the equivalent Cavalry civ if you're playing a Cavalry civilization). Attack and conquer the enemy civilization, remember they do have bonuses so you must be very efficient. Take good fights and pillage everything.
Point your research to Machinery, this technology allows for Crossbowman creation, which is a very powerful ranged unit and therefore very difficult to fight against only with Archers. Thanks to its huge Science bonus the AI is likely to have Crossbows sooner than you. You have to both weaken the AI before it happens and research the technology very fast.
At a point in the war you will have a huge prehistoric army that was effective before but not anymore. Upgrading is very expensive and that is why you need to have the Professional Army civic, which gives you a 50% discount on all units upgrades. Half the price is still pretty expensive for a war economy. The next two points are about how to get that money.
Sell all your surplus luxury resources, they do not give extra amenities and you usually can get 100+ gold from them (although selling for less is not bad either). In the same way sell all your Diplomatic Favor as it is almost useless early in the game. Units must be maintained and bought, gold is a valuable resource during war.
Make the enemy civilization pay for your upgrades. Although think it twice before pillaging districts, you will have to expend city production repairing them after. Terrain improvements are a safer choice, one worker is enough to repair every tile you pillaged before.
Don't get this wrong, use your envoys to be the suzerain of city states, but if you already are and can't get anything immediately then there is no reason to spend the envoys as you get them. Instead save them to flip city states in times of war or to get a city state with a very convenient bonus. Make clever use of the diplomatic slot, swap between the +2 envoys for your first envoy sent civic and the +2 influence per turn civic.
While conquering the first and second civilization you should score some wonders. Until you have production superiority (say top 3 score in the game and full industrial zones) don't waste your production trying to compete for wonders. Instead conquer cities that have them.
After conquering one or two civilizations you should be in a good spot. Controlling a good portion of the map and having more cities than any other civilization will allow for any type of victory you want. You should be near the top of the score ladder, if that is not the case you can either go conquer another Civilization or make really good use of your cities.
There will be land masses the AI has not settled on. Not only extra cities will add science, gold and production to your empire, but you will also be able to score strategic or luxury resources. Tundra zones are worth it too, you could find Aluminium, Oil or Uranium there later in the game.
Remember the AI has a 32% science boost. You probably are behind and should look to make alliances as the most benefited from alliances is the civilization that is behind (you). The same concept applies to Cultural alliances.
Any type of victory will require gold and production. Commercial and industrial zones are your friends. To get adjacency bonuses place your industrial zones next to an Aqueduct and a Commercial Hub, or even better next to 2 Aqueducts and 2 Commercial Hubs.
It is very likely that you are way behind in science. This is the time to build Campuses in every good location. The general rule is that if there is a location with at least +3 science bonus then build a campus there, if not, focus that city on other endeavors (culture, war, gold and so on). Mountains (+1 ) and Geothermal fissures (+2 ) are your best friends.
Late game is all about winning before the AI has the opportunity to do so
Those are the most sneaky ways an AI could snatch a victory from you. Domination and score are way more obvious and you will have enough time to react.
Either getting a Domination victory or preventing an AI victory Nuclear weapons and Giant Death Robots are your best choice. Nuclear weapons are great if you're somewhat behind in science. Giant Death Robots just make your life easier.