how to get full armor sets

I see online ppl talking about acquiring armor sets from various places in game, and I'm aware that sometimes you are rewarded with a full armor set, but aside from that, to get armor sets , is it just farming a type of enemy until you get all his armor? does every enemy type drop everything they have? I know wandering nobles have swords, and I have many types of breastplates and such, but I'm curious how it works.