How To Farm Pokemon Candy
Something every Pokemon GO player must do is learn to transfer multiple Pokemon of the same species. You will not be able to keep every Pokemon you ever catch, like any Pokemon Game, so it only makes sense to transfer multiples (unless they are both at extremely high levels and have great ivs). Usually, it is best to keep one of each species of Pokemon, the one with the better Individual Stats.
After transferring the Pokemon you feel is the worst among the two (or more), you will be given an additional Pokemon Candy for that given Pokemon species from Professor Willow. This is why you should keep catching the same type of Pokemon even after transferring Pokemon of the same species, what is often called Farming Candy in Pokemon GO. (If you plan on Farming XP by evolving a number of the same species with a Lucky Egg, then it is definitely okay to keep multiple of the same species. Just make sure you only keep the number of Pokemon of a given species that you have enough Candy to evolve, allowing you to not fill up unnecessary space in your Storage.) Rare Candies, obtain by defeating Raid Battles, can also be used to farm a certain Pokemon Candy, depending on how many of them you actually have.
farming is basically catching the same Pokemon over and over again and immediately transferring them, allowing a trainer to gain four Pokemon Candy for that species for every capture (even more if the players uses a Pinap Berry, as well as if the Pokemon is either a 2nd Stage or 3rd Stage Evolution of that given Evolution Chain). This method provides trainer the quickest way to evolve a Pokemon Species, and thus a faster way to accomplishing the ultimate goals of completing the Pokedex and reaching Level 40.