Though I'm new here, I have played Civ3 & Conquests a lot. It's been a while, but I just started a regent game and am having a jolly good time beating my neighbors to a pulp. I don't think any of these have been mentioned, but I had to sift through 20 pages. I don't remember all the details..
1 - Don't write off a start as bad right off the bat. Or good, for that matter. I have had excellent starting locations, but have had zero strat. resources; I have also had slow starts that happened to have the only iron and saltpeter on the continent!
2 - Resistors are annoying. When I capture a city, I usually make everybody a tax collector for the following reasons:
-the people will be pissed anyway, and the city will be in disorder. You aren't going to produce anything.
-assuming the city is fairly large, any [moderate] pop loss will be recovered shortly after the war due to the increased food surplus (from having less people). so after the war, there's not much to undo to get it back in action.
-you make so much money! handy for boosting research, happiness, or unit upgrades.
It's cold. It's heartless. It's totally my style.
3 - If you have a peninsula near you, cut off all access to it, then ignore it for awhile. (Unless of course you need a resource or something.) The AI won't be able to get to it for a while. Expand towards other civs first, then when they're stuck, you have this nice little piece of land to in habit.
4 - On a related note, if you have an area like a peninsula that no one is going to settle/explore, send some crappy units to look around. You do not want a massive barbarian uprising on your doorstep.