Here's an idea for you, then:
When the AI lines up its men in one solid line, it is always cavalry on their right (our left), infantry in the middle, and archers on their left (our right). You may want to look into changing this; it makes it really quite easy to figure out where you want to send your cavalry (right flank, to send at the archers) and where you want to bunch up your heavy infantry/pikemen (left flank). I can't remember if I've ever seen the AI line up in any other way than that. The only other tactic I can remember them using is just rushing me.
Edit (some of the best ideas come up in the shower, no?):
Would it be possible to have infantry, when ordered to bunch up, have the troops equipped with shields tend towards the front of the line, and the pikemen/two-handers just behind them?
It would also be nice to be able to tell my units to ignore routing enemies and continue fighting the unbroken ones. Or if you wanna get fancy, designate priority for routing units to individual groups. So I could tell my infantry to prioritize them lowest so they stay in the fight, cavalry to have normal priority on routing units (kill them if they're nearby but don't go out of your way), and my slavers could have high priority (so they ignore any non-immediate threat to go get me some slaves ransom targets)
One other small question:
Is there somewhere that details how spear bracing works? Either I'm aiming it wrong or the length doesn't match the weapon. I got one of them fancy Phalanx Pikes* with like 300 range and it seems more useful to just stab with it than brace. Bracing results in the horses dying when they're almost on top of me; stabbing kills them much further away (and the rider usually falls into the pike and dies from that too)
*This may be from pada's troop tree changer, but it's a no-shield polearm with 300 or 340 length, I forget which