I always expand slowly and sensibly. The only places I will expand fast will be in Germany and in India, because obviously they have a pan-cultural tag I can form that rewards rapid expansion, and then I stop AFTER I form Germany/India.
Conquest doesn't really pay itself off besides make other countries poorer. I like making colonial empires over contiguous empires (IMO they look cooler), so I have a shopping list of rich territories I can get, and then I develop them and field a massive Navy to control trade. I figured out I could make more money as a Japanese empire with less land than what they occupied in WWII, than a Chinese Empire that owned all of Eurasia without developing anything.