To get easy experience at the room in the Cursed Cave where you are supposed to throw skeletons into the barrier, instead repeatedly kill the skeletons as they continue to respawn.
How to defeat the spider in The Grinder:
To avoid being hit by the lava, go to the front. Press square when the enemies appear.
Easy kills hint:
In the Ruined City of Adoni, defeat the tortured zombies by pressing O + X to jump and downward slash.
To create extra essence, disenchant unneeded items instead of dropping them.