Enslave cities when you capture them. For instance, enslaving the population of Carthage into Lilybaeum kills two birds with one stone. Carthage has a lower population and Lilybaeum reaches the threshold for City status, allowing you to upgrade the core building and get a far higher public order. One quarter of the city's population is moved to your settlements containing governors immediately. Another quarter is moved over the next 15 turns. You can control this by moving governors in and out of settlements (eg. in the Brutii campaign, I can get Apollonia to Large Town inside 6 turns by enslaving Syracuse).
Temples to Baal can be upgraded to Temples of Saturn, don't just destroy them if you are going to upgrade the city soon.
Governors with high influence help calm restless people.
Public Health increases happiness, but increases growth.
Growth increases happiness, but causes overcrowding.
Recruiting a large number of Peasants reduces the population and increases the garrisson.
Games and Races are good for keeping the population under control.
Kill Egypt quickly. Take the Nile and eastern Med and you'll be rolling it in. You can then attack Greece to cut off the Brutii's advance and access to money.