I play on lower difficulty levels and mainly continental maps (planning to jump up another difficulty level next game probably). If I'm on a continent with only a few other civs, I'll attack them out as soon as I get to Axemen/Swordsmen. I'm usually forced to raze their cities due to maintenance reasons, but I like to wipe them out ASAP before they can build relations with civs on other continents - that way I get to war freely without a negative diplo modifier from the other civs. Plus, I basically get my run of the continent and can expand as far as my economy allows.
If there's a lot of other civs on the same continent, I'll only attack those who will threaten to take up too much of my potential real estate. For instance, if I'm on the norther stretch of a continent and I have one or two civs above me or squeezed in next to me, I'll set up a few cities to claim a slice of land, generally cutting off a part of the continent. Then I'll build a force of Axemen/Swordsmen and wipe out the one or two civs that I blocked in so that I can then settle their land at my leisure.