Im so bad at this game..
Im on Warlord level, and I cant win wars to save my life, my import/export demographic is is worst (and have no real clue on how to improve it) and I always get out-teched in mid/late game.
Right now, im using Elizabeth on Arch-type map, not a really strong military, aiming to try my hand at a Diplomatic victory, but my stats are awful, I have no real clue on how to play, but when I read the FAQ's and Newbie guides, they dont always make sense, or they are too advanced for my level of suck.
I have 18 Civs on my game also, is the number of civs proportional to how hard the game is, or does it really mean easier overcrowding?
Being good at war and being good at economy are two separate elements of the game although they influence one another.
To be good at war, you need to learn various aspects of the war mechanics of this game
1) use direct attack siege units against stacks (more than 4 or 5 units) to weaken the entire stack and then slaughter those wounded units with your own healthy ones. You'll lose a few siege units, but it's more cost efficient.
2) use counter units against lone units or uniform stacks of units. A stack of 3 macemen can be effectively beaten by a set of crossbowmen for instance.
3) bombard city defences before you attack.
4) use large stacks with a healer to preserve your units and don't let them be picked of one by one.
5) Always attack with ample units to take a city. It's a very bad move to sacrifice a set of units to almost take a city. You'll have lost more than your opponent and made his defenders more experienced.
6) Use promotions. Especially settle great generals and build barracks so that you get more experienced units than your opponent. If you typically encounter units with one promotion less, then your units will typically win at a 2 to 1 ratio.
7) If possible attack when you have a military technology lead.
Economy:
1) In the early game, there is a limit to expanding as you don't have the means to make every city profitable quickly. However, in the mid game after markets, courthouses and the extra trade routes from currency, almost every city that you build will quickly become profitable. And then more cities means more research.
2) The research slider doesn't determine the speed of your research, it's the science points production which determines the speed of your research. An empire of 7 cities and 40% science will typically research faster than an empire of 2 cities and 70% science.
3) Intercontinental and foreign trade routes are great. Open borders for better trade income. Don't watch the import/export stat. It's almost useless and can be misinterpreted very easily. Just improve trade by creatng cities on multiple continents/island (intercontinental trade), open borders (foreign trade routes) and harbors in cities with great trade routes.
4) Cottages and specialists drive your research. Cottages take time to develop into good commerce producers but become great after a while. Specialist research is based on research points created by specialists and research generated by great people.
5) A few extremely specialised cities with national wonders can do wonders for your economy. A great person city with lots of specialists due to a huge food production and a + 100% great person rate national wonder, a gold city with a shrine of a well spread religion with a + 100% bonus to gold national wonder, a production city with lots of mined hills and some food resources to be able to work those hills and a + 100% military production national wonder and a few settled great generals, etc.
A large number of civilisations doesn't typically make a game harder. If you can take out one of those small opponents who could barely expand, then you're already about twice as strong as most of your left over opponents. So you can rapidly conquer a few cities and already be much more powerful than your opponents.
A very low number of opponents isn't necessarily harder too. The AI can have trouble sensing the opportunities to claim a huge piece of land.