Hard AI - Random behavior. Pop either 200, 300 (testing strats for multiplayer), or unlimited (for just monster war fun). Starting RSS Low or Normal.
When it's on Hard mode - they've got a 25% gather buff, so they WILL have an army before you, 99% of the time. I find it helps to train a few cav (typically 5-7) at around 30-pop to do more hunting for food, but also to tank the first attack so archers/javs can knock it out. That first attack isn't usually more than a few units, so you can quickly grab everyone to fight it then return to work.
I've found as well, after watching some people in my multiplayer games, town setup matters. A storehouse on a border woodline WILL distract any troops controlled by AI enough for you to gather the forces to repel. houses close together helps break up a formation and funnel troops in one-by-one rather than a mass blob.
Hope that helps.