Civilization – What bonuses does a “deity” level AI get and how to deal with them

Apparently there is a flawless strategy in civ5 and if you apply it correctly, winning on deity is rather easy. And you don't even have to make some special settings for the game. Just I have to warn that its much more fun if you discover it yourself rather than get it from internet, as in that way it kind of ruins your game experience as it did to me to some level.

The easiest way (as Irony Man correctly pointed out) is setting the map type to archipelago, as AI is totally hopeless on water. Just expand all the time, build some naval units to fend off any aggressive AIs, grab those resources, trade and develop. You should be able to get any kind of victory quite easily.

You can also use continents or Pangaea maps. You need to apply a flawless strategy to get a win on those. A strategy might be slightly different depending on which faction you are playing, but there are some basic rules which work for all of them. The specific faction strategy is to get the most of the special ability. That means if you are playing for English - build naval units, if you are playing for French - build a lot of small cities, if you are playing for Romans - build all that is needed in Rome, etc.

The most important bit is a good start. I would divide it into three phases:

1. Settling. My winning initial build order is worker-settler-scout. Develop technologies needed to get those resources. Scout the land using your initial warrior and try to not be delayed by any spotted barbarians. Settle the land to grab the luxury resources asap, but don't go too far from your capital. Once you got a scout use it to discover map further and use your warrior to deal with barbarians near your cities. Get Liberty SP branch and Citizenship SP next. At this point you just build settlers, workers and monuments in all your cities. Forget about any early Wonders. If you met a militaristic CS you can steal a worker from them (they are useless). Declare a war, capture a worker and make peace all in the same turn. On the other hand its way too easy and some people call it an exploit, so I don't usually do that.
2. Fighting. At some point you'll meet other civs. Be nice to them, but don't forget that they are your rivals and sadly due to a crazy inherent AI warmongering its almost impossible to make a good friend till the end of the game in Civ5. You might be able to settle 2 cities or maybe 5 cities (depending on the map) before you start rubbing your shoulders with other civs. Discover archery and build some 2-3 archers. Discover horseback riding and build some 2-3 horsemen. Don't bother about infantry. Once you have 5-6 units declare a war to your nearest neighbour. Try to get other civs as your allies in this war for now. Do not attack! Select a good defendable spot of land (might be a river valley or similar), preferably inside your borders for a friendly lands fighting bonus and faster healing and get them to come. Don't lose any of your units, if necessary retreat to heal. AI should send several waves of units and run out of them at some point. By that time you should have discovered mathematics and built a catapult or two. Now heal your army and go and get those AI cities. Raze them and leave a capital as a puppet (annex it then you have some spare happiness). Settle the land with your own settlers. Now do the same to the next neighbour...
3. Developing. Constantly develop your cities, prioritize them. That means that some of your cities would be appointed to making money (if they have a lot of luxury resources nearby), some to making science (if they got jungle tiles), some to production (a lot of hills) to build wonders and units, some to make culture (none of the above advantages). You still need culture to adopt those all important policies even if you are not going for cultural victory. Dedicating city to some task means that you build that aspect enhancing building as soon as you have it available (markets, banks, stock exchanges for money cities, etc.) and you appoint specialists only to that same task. Still every city should have at least a monument, library, market and a coliseum. Make city-state allies. Preference is for not hostile ones with a luxury resource you don't have. After you make allies with several maritime CS's you can stop building farms and better build trade posts. Then make allies with cultural CS's. Forget about militaristic ones, unless they have a resource you so badly need.

Now if you still haven't lost your army at this point you should be doing rather well and can continue playing the way you like. Or if you want to be really effective and crush them all you can apply an ICS (infinite city sprawl) strategy. This strategy is genuine and it works perfectly, but honestly I don't like it myself at all, as it takes all the fun off the game. So if you enjoy Civ5 so far and want it to continue better close this post now, but if you want to further ruin your game experience read on..

The basics of ICS are explained elsewhere much better than I would be able to, so I'll just quote. Here's the theory behind Infinite City Sprawl, as written by alpaca in his Infinite Rome thread on Civfanatics:

The idea of an ICS strategy is to settle cities as close as possible to leverage the additional growth, production and commerce that small cities have over large ones. In Civ5, there are a number of game mechanics that lend themselves well to this kind of strategy. To wit:

1) Maritime city states. The bonus granted from maritime city states is per city. Each adds +2 food to the city tile at the start, increasing to +4 over the course of the game. Since every city benefits from this free food, a single maritime CS ally will allow you to set up two additional specialists in every in the later stages of the game. Obviously, the more cities the better, because each gets the bonus.

2) Happiness buildings. In Civ5, happiness is global... or is it? In fact, only the consumption of happiness is really global. The production is local. Each city can build happiness buildings, and the low-tier buildings are more efficient and more effective than the higher ones. If you have lots of small cities, each can have a Colosseum and a Circus where available, and some theatres. This actually rules out happiness as a long-term limiting factor and turns it into a growth-limiting factor because you need to set up these buildings in each new city.

3) Purchasing things with gold. Provided you have enough gold, you can buy buildings where and when you need them. Spamming trade posts is a typical strategy, and it's possibly even better in ICS. Just spam trade posts, make money, and buy the buildings you need. This is especially good for the more expensive buildings which have a better gold/hammer ratio.

4) Certain policies, like Communism and much of the Liberty tree, scale with the number of cities. So do some civilization abilities or buildings, like the one of Harun al-Rashid or the Chinese Paper Maker. For them, you also want as many cities as possible.

5) Research favors large empires because a tech will cost the same, no matter how many cities you have. Since having more cities usually means having more science, you will tech faster.

6) Trade route maintenance makes you want to put your cities as close together as possible. City tiles are free roads, after all.

There is a significant drawback to ICS which I won't hide from you: The speed of unlocking social policies. This is the only thing that is really better for small empires because, roughly, your average culture per city is what determines policy speed. Since there are sources of culture that don't scale with the number of cities, like wonders and cultural CS, you will be slower at unlocking these SPs, so make sure you only pick those which are most useful to you.

You can find some great comprehensive examples of how it is applied here: http://www.garath.net/Sullla/Civ5/liberteordre.html or here: http://forums.civfanatics.com/showthread.php?t=390302 and this one is very short and straight to the point: http://forums.civfanatics.com/showthread.php?t=388793