This is a very loose question.

How do you approach the balence of expansion/war in your games?

On the lower levels you can simply outexpand the AI and by the time the get to about 4 or 5 cities, you can easily crush them with units that are at least one era more advanced. One exception though, if they happen to control a resource or if they're just annoying you just crush them right away.

On the higher levels I tend to make sure that my defenses are up before I attempt any offenses. It all depends on how many cities I have at the moment of contact. Sometimes I might even try to rush them.

For me, it goes like this:
1) Expand until I'm out of room.
2) Kick back and build horsemen until I've got MT and sometimes SP.
3) Kill all their dudes, burn their cities to the ground, enslave the woman, eat the children, plunder their treasuries, seize control of their wonders and drop my own settlers all over their territory. Die! Die! Die AI! Die!
4) Switch to decaf.
5) Milk.

If you are serious about milking and get settler factories going, there is no reason to start a war until you have grabbed as mush land as you can IMO.

I really haven't thought about it much since I usually just play the game to see if I can win and then milk once I get control of the game.