Don't be stingy with Psi powers. Magic Butterflies are commonly encountered in dungeons.

Grinding is easier after defeating the boss of a Shining Spot dungeon. The enemies there run from you so it's easier to get surprise attacks and insta-wins.

You can only get the Sword of Kings before defeating the boss of the Stonehenge base. All the monsters in the area vanish once the boss is slain, and the weapon can no longer be obtained. That said, Poo is plenty strong without it - None of the super rare weapons/armour pieces are necessary to complete the game.

Psi Thunder is powerful but often misses. As long as there are at least four enemies remaining, it's guaranteed to hit at least one of them.

Managing your inventory by phone is a pain in the ass. If you visit Tracy at your house, you can swap items in and out of storage at will.

The hardest part of the game is before Paula joins your party. Don't lose heart if the game feels too tough until then.

You don't have to call your mom regularly to prevent homesickness. Homesick happens completely at random, whether you just talked to your mom, or haven't spoken to her for the entire game.