Genetics is the most important thing to get buds with a ton of trichomes. Other than that giving extra PK in the form of a pk booster will help as the plant generally needs a lot of pk in flower for bud and trichrome production. You could also try dropping your temps. It is speculated that lowering temps the last few weeks of flower simulates wither coming causing the plant to up resin production. It is also speculated that low humidity(30% or so) will do the same thing.