1. Go easy on the fighting until XBs. Make a ton of units (hence 3 cities that will grow - to increase 'supply') and train them on barbs, a vulnerable city state, or an AI that can't war properly. But trade with everyone else, and try to grow those 3 cities. Build markets, universities and eventually aqueducts.
2. But delay Construction as long as possible, and then immediately tech to Machinery and hopefully it will coincide with the Honor finisher. Then start taking out capitals and do whatever you can do to keep growth going at home while building mainly units & important stuff like workshops.
3. After Machinery, tech to Chemistry, and then Oxford into Dynamite. The Commerce tree will help a bit, but the main thing should be the Honor finisher helping pay for stuff. Save money for 3x factories for when you hit Industrialisation (right after Dynamite). Next turn choose Elite Forces and more importantly Mobilisation. Build Big Ben after that, but really, Mobilisation, the reduced purchasing from Commerce and the Honor finisher is completely awesome. You'll earn a 1000 gold a turn if you do it right and you can spend it straight away on elite troops.
4. After Industrialisation, if you have capitals you need to take out with ships, go to Navigation. At some point Peddro suggests selling universities, but I'm not sure when the best time to do this is. It's probably situational.