You go in front of one of the treasure chests in one of the places where you find monsters.(Only on seirtain treasure chests) You`ll find a monster. Then you move away, then go in front of it again,and you`ll end up finding a monster again. Just keep doing it over and over again, fighting and defeating the monsters to gain levels quicker. For example, in the Cavern of Earth B1,go in front of one of the two treasure chests and you`ll find an Earth Elemental 1. Defeat it to claim 384 EXP and 768 gil. Move away from the spot and move back to the spot. You`ll find the same monster again, and defeat it to claim the same experience and gil. This is also a way to get loads of money. Repeat this stradegy to gain levels quicker.