Some ways that I think will improve AI's skill:
1) As other people mentioned, get better units other than a large number of miserable militia or slingers. This will probably help a lot.
2) Use human pre-designed pretenders. AI use insensible pretenders. We can easily make a wide variety of pretenders, catered to the play style of AI.
3) Teach it how to use super-combatants. Among various human tricks, this one seems to be the easiest to teach AI. Put a few items on a big creature and send it out. This, combined with human-design pretenders might help AI use their pretenders more effectively.
4) Castle? I don't think AI build castles on important provinces.
5) Other tricks? For example, it's quite easy to tell human to aim for "Storm" & "Wrathful Sky" combo. How easy is it to teach AI to aim particular spells like these?
There are strategies that are simple but very effective. For example, a Jotun with a simple Wyrm and maximum scales, keep building Woodmens, Seithkona and aim for Evocation 7. Another example is to use a basic Prince of Death for Ulm, aim for "Boots of the Behomoth". Put the heavy Ulm armors and the "Boots" on the PoD and send him out.
Are there any ways to script such strategies for AIs? Or should we start designing a scripting language for Dom AIs

?