OCC has changed quite a bit in BTS. With the addition of National Park the only thing that limited the city before BTS is now gone. For balance purposes you can now only build 5 national wonders, so there are some decisions to made now about what to build instead of simply everything. The first crucial decision in an OCC game is what map to play on. One of my favorite parts of an OCC game is seeing the huge amount of land that you city covers once it is legendary. So that means that I don't want to be near the coast. Since I'm not near a coast I won't be able to build any boats, ever. This means playing on a map where you can get to everywhere without having to use a boat. I prefer to play Pangea with pressed shores so there are no islands. The size of the map is crucial. When you play on a huge map there are modifiers to the tech speed to make it slower since everyone can have more cities than a standard size map. Since with OCC you will only have one city, this is a big disadvantage. I play either standard or small maps. It helps if you further cut down on the amount of cities the AI civs have by adding a few more players into the mix. I usually play with 8-9 civs on small and 11-12 on standard. The other big decision before the start is who to play. In normal play my favorite leader is Random, but I don't think much of him for OCC. So many traits are totally or mostly useless in OCC that I always choose a leader. The traits that help you fight really aren't that useful, going out and taking over huge amounts of territory just means that someone else gets to expand into that area. That means that Aggressive, Charismatic, Imperialistic, and Protective don't really work that well. The secondary bonuses of these traits aren't that useful either, though Imperialistic's faster settler building is as worthless as it can be. The happy bonus of Charismatic would be useful early, but happiness is not a long term problem in OCC. Organized is totally worthless as civic costs are always 0, and a half price courthouse (just one) isn't necessary since city maintenance is 0 also. Creative doesn't help any since the city will be a cultural monster whatever you do. Surprisingly, Financial isn't really a big help. If you do go the cottage route since you will only have the one city they will all mature relatively early in the game. Once you get to towns they will peak at 5-6 commerce per town, since with financial that will only be 6-7, the percentage difference is just not that great. Financial makes the biggest difference when you have a lot of tiles that would generate 2-3 and they get boosted to 3-4. But at least it does something. In Warlords, Expansive was an excellent trait to go with. Health problems start fairly early and persist through the whole game. If you play with an inland capital like I do then you probably wouldn't see any health boost for seafood until you built the Globe Theatre and could trade away happiness resources for them. But with the drop in BTS to +2 health from +3 health, and the addition of the National Park. I no longer think of Expansive as a top tier OCC trait. I'm already missing playing as Isabella. Industrious is a great OCC trait. For one thing, you are going to build 5 national wonders. Industrious will save a lot of time there. And at the level that I play at, Monarch, you can definitely grab a lot of useful wonders. You aren't going to making huge rampaging armies, no settlers, and your infrastructure buildings just have to be built once. So you can put some time in building wonders. Philosophical is the other choice for an OCC trait. My last game I was Industrious and I still never built a cottage, just ran specialists the whole game. Obviously this would work even better for generating GPs if you are Philosophical. What you do with all of the GPs is up to you, but settling them seems to work better in OCC than a normal game. Since there is no leader who is both Industrious and Philosophical, you have to choose one of those and another trait. Since Expansive has lost some of its effectiveness in OCC, that means Spiritual. Spiritual is one of my favorite traits anyway, but it reaches a new level of effectiveness in OCC. You don't have to say 75% of my cities are building buildings so I'll be in Organized Religion. Since there is only one city you can always be in exactly the right civic for what you are doing. Plus, temples are half price, and they are one of the few buildings that you build more than one of. That is kind of a joke, except it isn't funny. Some of the victory conditions just don't work. You can't get cultural or domination. Unless you turn on permanent alliances, in which case you can. Time victory is a weak fallback, since your civilization is going to be so small the chances that you can win a time victory after not winning some other way is pretty slim. Space race is usually the easiest, it is perfectly strait-forward, you tech your way to the parts and then you build them. Key to being able to do this is being on a smallish map. Conquest is also possible. Maybe you could start on this early and take some civs as vassals so that other civs don't get too big, but I've never really tried that. My conquest victories have come by going on a rampage around the time that you get tanks and just wiping out or vassalizing everyone in one big long continuous war. Diplomatic victories are certainly possible, and they will be true diplomatic victories, not you voting for yourself because it is quicker than finishing the domination. Your votes will be truly insignificant, you have to be loved by a majority of the other nations, and you have to build the UN yourself. To go that route will definitely give a workout to the spiritual trait.