Have the Judgment Staff in your inventory so that Flare can be easily cast. Have all but one character dead in your party, and to be safe have that character be at least level 50. Then, go to the second floor of the Chaos Shrine. Fight Green Dragons and Black Knights that reside there. When in battle, use the Judgment Staff to cast Flare, which will instantaneously kill the foes (although a second round of Flare casting may be needed). The experience points (EXP) dropped by the Green Dragons and Black Knights is staggering and will allow you to quickly level up your character, one at a time.

When your party receives the boat and can go on water to fight water-based enemies, you will be able to easily level-up. Find a place where you can travel around the entire world map via water without running into land. Tape down the directional button and the X button (or put something else heavy on it), making sure your party is around level 20 or higher in order to withstand the attacks that will occur. Then, walk away, keeping the occasional eye on the game to make sure your party hasn’t been slain. If done properly, your party will quickly and easily level up in this way.

After unlocking the Earth Gift Shrine (by relighting the Earth Crystal), head there to find an item that increases your life permanently by five (it’s in the desert section of the Shrine). If you continue on in the shrine and lose to one of the four bosses within, it will send you back to the beginning of the Shrine, but you’ll still have that item. What’s more, you can get the item again when you proceed through the Shrine once more. You can repeat this process over and over again to get the item as many times as you want!