Look up Ecothrive charge mate if your in soil, you won't look back. A good compost tea packed with macro nutrients and look into suplimenting your soil with the right amount of sulfur. (If all other factors coinciding)
Obviously genetics and environment but if you have them dialled in look at macro nutrients,in my opinion sulfur is a killer for trichome production in the right dosage. You could make a DIY feed but feeds like Turpinator that have already been mentioned are easier as all done for you.