I got all the achievements on it, Huns on Asia were fucking hard.
The opportunities that give you bonus yield on tiles are the most valuable you can get because the bonus stacks with your research.
AI doesn't get opportunities at all, so when you play harder civs, making effective use of the ones you get is key to victory.
Don't get military unless you absolutely need to because it's expensive.
Invest in yield, pay money to lower waste (a certain percentage of your stockpile gets lost every turn due to waste, reducing it is important).
In the early game, don't save up resources but spend them ASAP, stockpiling is ineffective due to waste.
Researching power technologies gets exponentially more expensive, but is extremely important in winning fights. Each power tech level gives you +1 strength in the respective terrain type. Got a mountain border with a strong enemy? Pump mountain power tech.
Sea is expensive to claim, and sea yield techs are expensive to research, but most maps with an ocean have lots of sea tiles and most AI won't care about the sea (unless they're an island nation) so much of it has little contest to grab. Even though sea never provides a lot of yield, a ton of sea tiles translate to a ton of yield once you have the tech.
Sea tiles have zero yield without tech though, so don't prioritize it early on.
The tech window tells you exactly how many resources you get from each tile type. Obviously, since techs apply to tile types, it's more profitable to acquire tiles of the same type. If you got 40 forest tiles, researching a forest yield tech of +1 gold per forest gives you a whopping +40 gold, while if you only have 5 plain tiles and get a plains yield tech that only translates to 5. Simple maffs.