I usually pop For the Horde when I begin to see Barbarian orcs starting to spawn. Any Scorpion Clan units I get are worth trying to keep, the rest I only keep situationally (ie depending on the damage they are doing to my economy). Goblins will try to seek out wolves, orcs will explore. Most of those will end up dying quickly anyway. My aim is to find a Goblin Fort near another civ's capital (close to mine, if possible), and get as much gold as possible from tribal villages. I'll buy 20 or so goblins from the fort and crush my target civ, keeping the capital if it is close to me or razing it if it is not. Then, depending on available funding, I repeat with another civ. Once practical targets or gold are exhausted I'll disband any unpromoted units (except for Wolf Riders and Scorpion Clan units) and draw the rest back into my territory.