The Grinder - Defeating the High Priestess
The easiest way to defeat the High Priestess when she has assumed the form of the spider creature is to go to the front of the place where you are fighting so you don't get hit by the lava coming at you and keep pressing Square when the enemies appear.
If you need to make extra essence, disenchant items instead of dropping them. Don't do this with needed items.
Easy Experience and Tortured Zombies
Get Easy Experience:
Reach the room in the Cursed Cave that you have to throw the skeletons into the barrier but instead of throwing them kill them. The skeletons will keep respawning and you will be able to gain as many levels as you want.
Defeat Tortured Zombies:
The easiest way of defeating the tortured zombies at the Ruined City of Adoni is to press Circle and X when you engage in combat as this type of jumping downward slashing attack will inflict 90% damage on them