Keep RH around 40-50%.
UV exposure during flower can increase trichome production. If you have UV in your lights, you don't want it on during vege phase or even early bloom, i bet. It's a stress that causes the growth of trichomes. It will adapt to UV and be resistant to it, if you expose from start (like field crops do -- this is why initial studies showed it did not help.. they were testing plants out in a field and exposed to sun from sprout, which have developed resistance to UV.)
Certain stresses can cause it to occur. heat, low rh%, UV rays etc etc... but becareful not to piss off plant and grow nanners in your quest to augment trichome production. I'd becareful with heat. The RH suggestion is safe.. uv should be safe, for the plant (do use precaution for yourself, as UV will cause skin cancer.)
in the end, any technique you use is always relative to genetics. Can't put lipstick on a pig... well, i guess you could, but it's still a pig. Not a reference to your plants, but explaining concept.