well there is a product design for resin production. Purpinator and terpinator. They worked well for me (when im not having my nightmare issues in my grow) i had to use alot of it tho. I had a mother purple punch i was doing test grows with, the first cuttings turned out like alright bud but when i went from that grow to a new one with terpinator it turned up the resin production from what i could tell. but as many have said thats more of a genetic thing. cant teach an apple to be an orange. but if there is a decent resin production already it can be improved through temp, humiditiy ( epically after harvest) nutrients, and sometimes plant size. but from what I've experienced smaller plants seem to have more resin, but that could totally be environmental or human error.