[PvK]

I generally turn up the supply multiplier to help the AI not starve its large armies.

I also roleplay my nation, which limits my choices, especially when playing Ulm.

I think it may also help to have a large number of AI opponents. Then the ones that have bad luck don't really matter, and the ones with good luck can really get large and powerful, and you can end up at war with several of them at once.

Hard research and low magic sites are also probably in the AI's favor, maybe higher resources and gold as well, since the main way players outclass the AI is their ability to concentrate on the most effective magics and use them well.