Okay, to the experienced players here, these will no doubt be pretty standard and well known. However, for any newer player they may come in handy. 1). If you have cornered the market in a luxury commodity e.g. sugar, try and ally yourself with any City state that may have the luxury. This ensure the AI needs to trade with you to obtain it- you can have a greater range of luxuries to select as the AI generally has far more territory than a city state. 2. If you are in a war with the AI attacking your city and you have adopted oligarchy (where your garrisoned units increase the city attack strength) ensure you garrison your troops before firing at th enemy. By this I mean if you have a crossbow that fired the previous turn, regarrison it before using the city attack. You can then use the crossbow after the city shoots (this will give an extra point or two to the city).