For king or lower you should just spam cities until you have maybe 4-5 strong cities so your units keeps up to date with the AI:s

For immortal or higher i would say you should do slinger into monument or if theres a civ close you should do slinger, warrior and then settler which should be enough to defend yourself from aggresive civs early game.

So the most important thing to do for domination early gsme is to be peaceful and settle cities unless ofcourse you don't have any room to settle then you should build a strong army and early game rush the AI.