If you equip the Cursed Ring and a set of armor that offers elemental protection. You will now absorb the damage from that element at the cost of reducing your physical defense. For example, when used with the Dragon and Crystal Armor it will absorb all elements.
Avoid physical damage
Cast the Blink spell (White Magic) on your characters to have them immune to physical damage for a short amount of time. Rosa, Kain, Ceodore, and Fusoya can cast Blink.
Completion bonus
Successfully complete the game. Load the cleared game file and continue the game. Go to Namingway to play new challenge dungeons. There is one for both the base game and Rydia's Tale.
Easy "Twofer" achievement
Defeat the Lunar Dragon in the Lair of the Father B3 in the Subterrane. Next, have Palom, Porom, or Leonora learn Dualcast. Leonora is recommended as she gets Black and White magic and is a better White mage than Porom. Place the character that learned Dualcast in the party and start a battle.
Easy battles
Use the Stone Blade, Medusa Arrows, or other weapons that can cause the enemy to slowly petrify.
Gameplay Guide
Exploring dungeons completely - watch the percentage counter on the lower touchscreen - gives you a few items for your troubles, and is almost always worth doing.
Keep it simple in action as front rows are for fighters, back rows are for the mages. Back row members take less damage from physical attacks, so keep the weak ones back.
When grinding through easy battles, just pop the game into auto and allow your team to do its thing.