Farming souls is easier than farming bloods, since a soul does not need a special block nor does it get blocked by any block.
The easiest way is using a monster-grinder (especially a Soul Cage grinder), just wait until there is a lot of mobs and use the Reap ability, all of them will die (except infernals), and it can fill your Soul Crucibles very fast.
A harder way is by finding a battletower and just battle using a SoulSteal enchanted weapon, you can get over 5 souls when you 'finish' the battletower.
In multiplayer, having one person to kill mobs and another to bring a lot of Essence Keepers and collect the souls is also a preferred way.
- Bosses drop copper-colored Souls, and collecting it will fill a Keeper of Vessel to full capacity instantly, it is recommended to collect it with an empty Keeper or Vessel.
- Harbingers drop green souls, these souls are worth ten regular souls.
- Spectral Miner spawns as a soul, upon an attempt to collect the soul, the miner will appear and attack the player.