There are a couple annoying bugs with AI that even experienced player can't really work around:
1. Units attacking walls when there is an opening nearby - this is not something you can predict or counter, short of wasting a rally and wasting time for other troops as a result.
2. Melee units that gained range in later ages (footies, tanks) will often come up to target to point-blank range before retreating back to their real range before starting to attack. This results in unit taking unnecessary damage and possibly dying before beginning the attack.
Let me bring in my pet peeves, this is stuff which could easily be avoided if my troops at least played like any other AI. I mean, it's ridiculous what we still have to put up with.
First, the suicidal supply carts; they don't care what's in the way, there might be a dangerous tower or anti-tank gun, they're still going to find anywhere there's an opening in the wall and charge through there without regard for their own lives. This gets at least one killed most of the time. Sometimes my opponent hasn't realised that there's a hole in their wall and doesn't have many defences up there, but that's more at fault with them. I remember a while ago, some bases were designed to exploit the terrible AI on supply carts. They also will rush to heal singular units, prioritising a small group of shooters that went to attack something far away over my large group consisting of the brunt (75%+) of the army. Jesus...
Seems like cannons also don't know how to stay out of range. I've seen them destroy towers and castles without getting in the way of their shots. Most of the time, they're defended by a Singijeon that gets in the way of the tower's shots and rescues them, but usually when a cannon goes off by itself to attack a tower I need to use a rally to ensure that it doesn't get killed. This can get pretty infuriating when I don't have rallies or I'm trying to do something else but I need to save one stupid cannon from its own accidental suicide.
Lastly, shooters ignoring defensive troops. Sometimes I'll have a stray pikeman or whatever attacking a supply cart or cannon. Usually this isn't terrible since they either get shot by a Singijeon that was late to the party or once I rally they follow my army but get obliterated as they check their back and eliminate any remaining troops. On some occasions though, an entire row of Singijeon ahead of supply carts and cannons fail to save them from getting killed by an iron horse or two or some rubbish classical defender. This contradicts the entire purpose of shooters, but it's nothing short of infuriating when I don't have a training blessing active but I'm still trying to attack with minimal wait times (meaning don't let any healers/siege die). Simple AI improvements would make attacking so much more efficient for me.
And yes, I have tried rallying onto a wall to make sure that one gets destroyed. My army doesn't go in through the opening as you'd logically expect. They usually spend time destroying some other buildings around the other walls and still split up, rather than getting INTO the walls and then splitting up. Having this little strategic control over your army is insane, especially when the IA isn't competent enough to deal with itself sometimes.