Pokemon Nests
Besides hatching eggs, the best way to obtain loads of a given Pokemon's Candy in order for evolution or power ups is to find what is known as a Nest in Pokemon GO. Nests are given areas, usually a park or other similar area, where one specific Pokemon Species spawns (appears) more often than usual. Normally, Nests are defined as any given area where ten or more Pokemon of a given Species appears within one hour. Sometimes these are scattered from hour to hour, but sometimes a cluster (five or more) Pokemon appear all at once.
If you discover a Nest or find one online in your given area, you must act fast and take advantage of this while you still can. This is because Niantic usually changes the spawning pattern of all Pokemon every month or two, commonly regarded among players as Migrations. After a Migration, Pokemon, primarily Nests, are swapped with at least one other Pokemon to appear instead. A Nest of Charmander could be there one day, but after an unforeseen Migration, that Nest could turn into nothing more than one for Rattata. Nests also allow players to complete the process of chaining in hopes of increasing the odds of finding a Shiny Pokemon - if said Pokemon can be found in its Shiny Form - done by only battling one species of Pokemon over and over again.