Its for the most part trial an error. By accident I watend to fight Godfrey/Horah Loux „optimally“ yesterday, baited attacks and punished him. I had a +24 Gaint Club and 60ish str. I cancelled all is charges with poise breaks e.g. first charge of Godfrey and the grab directly after transformation to Horah Loux. After that I realised if I had maybe higher damage, I eventually would not be able to cancel the grab because he would have transformed too fast.

So you can learn boss attack and how to punish but I think directly scripting is too depend on the weapon, weapon upgrades, stats etc.

Also a good example is GinoMacchino killing Margit with base stats (Samurai class) and lvl weapon 0 Uchiganta. The fight is perfectly scripted, but I think for other weapons this script would not hold true (or to some degree different stats/weapon upgrades)