[Aiken]

It involves modifying AI scripts, which are placed inside Races folder. Most important and complex script files are RaceName_AI_Construction_Facilities.txt, RaceName_AI_Construction_Vehicles.txt, RaceName_AI_DesignCreation.txt, RaceNames_AI_Research.txt. Tweaking of RaceName_AI_Planet_Types.txt and RaceName_AI_Fleets.txt are quite important too.

Good thing is that script syntax is very simple, bad thing is that building good AI involves a lot of workarounds, non-obvious tricks and pseudohacks. Also don't expect to find comprehensive FAQs, HowTos and such - documentation is quite limited. Best way to learn AI modding is to grab mod with good AI (TDM, AIC, Trek_Bab, DevNull - those I have played) and start to read its scripts. Then modify something and see what'll happen.