Here's a few tips I've picked up in my own learning. I'm still on Prince, too.
1) Specialize your cities for either gold or production, not both. (Research in CiV is separate from gold, unlike any previous Civ game, and based mostly on population, so you want plenty of food coming in to every city.) No more than 25% of your cities should be production cities, although your capital should definitely be one of them. Production cities get mines or lumber mills everywhere they don't get a farm. Gold cities get trading posts instead. MOST of your cities should be gold cities, but you want a few production cities to quickly produce units, wonders, and spaceship parts.
2) Use the focus settings. Once your gold cities get above about 10-12 population, set them to "gold focus." Put the production cities on "production focus" under the same conditions, unless they starve when you do. (You can also micromanage by picking exactly where to put your people to work, but I haven't found that to be necessary.)
3) Make contact with all other civs, and trade luxury resources like crazy. Any luxury resource you have 2 or more of, only 1 of those makes your people happy but you can trade the excess for luxuries the AI has more than 1 of.
4) City States usually have resources. If you become an ally of a CS, it will send you gifts of its resources. Look for City-States that have luxury resources you don't have. Become their ally, and it will help your happiness.
5) Look over the Policy Choice trees. There are choices in just about every tree that help happiness and/or gold. The biggest one for happiness is Piety and for gold, Commerce, but there's something in all trees that's good. For example, in Rationalism, one of the choices gives you 1 happiness per University. In Commerce, one choice gives you 1 extra happiness per luxury resource.
6) Trade routes -- when you connect a city to your capital with roads and/or harbors, you get a boost to gold income that's almost always more than the upkeep cost of the road.
Hope that helps.