Contact to a warmonger-Civ within the first 10-15 turns or so, even if I don't know where they are yet -> Insta-DoW. I know I'm not going to like them and they're not going to like me, nobody is going to have a DoF with them and I haven't met any other Civs yet, so it's basically a free DoW. I'll usually use my first 2 Archers to pick off their units, farm exp and make sure that they can't expand, steal a worker if possible etc. Doesn't really work on Deity, but it does on any other difficulty.
I'll usually not try to take Capital though - except if it's in a REALLY good spot - and instead use them to level up my army as much as possible.