This little trick will help your mage level up and get some money with relative ease. I know there have been several similar threads posted before but this is more of a basic overview.
So, in this example our mage is lvl 27. You need to find the lowest lvls that still give experience, so for our mage around 20-21. You then head to an area containing a lot of these and aggro a large amount of mobs. You then need to mana shield yourself, and Arcane Explosion spam until there all dead. With patch 1.11 Arcane Explosion has an instant cast so you can use it without fear of interruption. When they are all dead pick up your loot and repeat
For higher lvls, you may want to simply use it on enemies around 5 lvls below yours to make the most money and xp.