Spend at good long time in each area fighting monsters to level up. I suggest leveling each individual costume to 100% before going on to start leveling a new one.
Remember to visit each area over and over again. Especially visit the areas that are no hot spots before visiting the hot spot areas. Even when i mission is complete there is usally still alot to do in the area and alot to find.
Check everywhere and talk to everyone several times. You'll be suprised with some good items sometimes.
Any questions, ask em, i can probably answer em.