lots of methods. slow liver metabolism or clearance, alter inherent pharmacological properties etc.
many terps can be added or used in conjunction but have little actual effect on a "different" high. you can increase certain properties. benzos hitting gabba, smoke weed which also hits gabba will intensify these effects.
hallucinogens dissociatives are the best to mix to actually get a dif high. you can turn weed to a full agonist and its pretty different at that level, just like jwh