Here are a couple of good places to earn some nice EXP:

1. Sinchon - Fight the Bots here to earn great EXP. Begin using elemental attacks on them. ie: Wind + Water, etc. The Bots will then "burst open" and their EXP will double in value. Heal them up, and wait a couple of turns until they repair themselves, then continue using elemental attacks until they burst open again and repeat the process until they have a maximum of 65,355 EXP! NOTE: Make sure you don't kill them too early, so try using Lv.1 spells.

2. Mt. Yogy - Fight the Lavoids here to also earn great EXP. Using fire attacks on them will increase their EXP value. Be warned though, they become more powerful with each fire attack you use on them, so if you feel you can't defeat them, then stick to the Bot method. This Lavoid method is pretty much for advanced players. Anyway, it's best that you use Molotov's on the Lavoids until they reach the maximum of 65,355 EXP. At this point, the only way you can defeat them is by using Super Combo. That, and you'll need some power up items such as Ginseng and the skill "Focus" for the additional power you'll need to defeat them.