Sorry I can't help you

.. because I can not see or know which area you have tryed yet...
... which skills you used (humanform), your stats...
But if you're level 20 it must be possible to kill some Goblins level 21 ... have you met these kind of Goblins level 21 to 23?
I use always a combination between Ranger, Mage and Warrior. Magic Blast is realy great! Ranger Stealth too!
So I used first a bow and via Ranger Stealth I can focus on an enemy before the enemy see me! So I on that moment make the spell Magic Blast and than begin with poison Arrow and shoot with my bow! BUT, I walk backwards so the other enemies don't follow!
From the moment that 1 enemy is close by, I take a sword for the final blow!
If a Healer heals that enemies HP, I run back and try to focus first on that healer and give him a Magic Blast héhé and try to kill him first!
If an enemy shoot ranged attacks or spells to me, I jump or roll away from these attacks ...