One of the things I found when I moved up to Emperor level is that, for me, it's almost impossible to win without fighting an early war and putting your nearest neighbor into a permanent, inferior position. As soon as I get iron, I start cranking out vetern swordsmen, with some veteran spearmen ('cuz they're cheaper), and I go after my nearest neighbor and try to take 1-3 cities. I especially try to get a luxury resource I don't already have.
So while I like to build up, in that first war I always fight, it's not possible. I get strong enough to take something and hold it, and then go for it.
If I have a UU that comes into play in the middle ages, it's a bit easier to be fully prepared to achieve my strategic goals quickly. I often fight a 3rd war late, and I'm always ready for that one.