As a mage... Dying is very easy and frustrating. So I'm here to help you out =)
Levels 10-15 Goblins in Rokoko Mining Cave is a good choice. If you are fully built off of INT you can practically one hit them.
Levels 15-30+ Skeletons in Forgotten Cave is a decent place to level if you don't have any good armor and weapons. Even with them it's a good place to begin at.
Or you could go to Rokoko Plains and find a party and farm "Broken Staffs" from Baums until level 30+.
When your level 30 there is a quest In Capital City Sofya at the Guild Hall in the Consulate. There will be an NPC there named Napherta. She gives a quest called "Impromptu Arrows".
If doing the Broken staffs which require 30 of it to complete the quest, will give you 7,500 experience and 1,000 spina. So if you save up to around 40 stacks (Broken staffs ×99). You can easily hit level 45+
Then just repeat this quest or you could go to Venia in Rokoko Plains and take the quest "Shadows of the cave"(or something like that lol) and kill 30 skeletons for 4,500 experience.
I' at lvl42 right now, a lot of my leveling was done in Forgotten Cave. Doing "The Forgotten Cave" and "Blacksmith's Hobby" quest. I'd usually start out kill Gargoyles, then as I pass through on the way back to claim the prize, I knock off 30 Skeletons.
I'm look at other quest now to up my EXP. I am currently working "Vengeance Attack".