1) Take all the equipment off a character
2) Place the character barely within range of the enemy boss
3) Make sure your character has enough defense/resistence to take as many blows as the boss deals out
4) Place a healing character behind this character
5) Allow your character to be hit
6) Heal your character with the healer that was placed behind him
7) Repeat steps 5 and 6 until your enemies' weapon breaks
8) Equip the character and have them attack the boss but make sure the boss will not die in the number of blows that he is hit by
9) If the boss will die in the next blow, wait until they fully heal
10) Repeat steps 8 and 9 until your character reaches level 20 or all his weapons break
11) Repeat steps 8-10 with each of your characters
The second experience trick is known as Arena Abuse. Arena Abuse is a lot more rewarding then Boss Abuse because you also get very rich off of it. Remember the following information when fighting at the arena.
Below 600 Gold: An Exceptionally Easy battle
600-699 Gold: An Easy battle
700-799 Gold: A battle of Mediocre difficulty
800-899 Gold: A Hard battle
900+ Gold: A Very Hard battle
In Normal, an Arena is usually easy, but in Hard Mode, it's very difficult. Any character who has class changed or is a prepromoted character will actually recieve a lot of experience because the Arena matches them up with a good computer character. If your character is facing a Swordmaster, yield if your character will die if the Swordmaster will kill him with a Critical hit on their next attack.
VERY IMPORTANT: You can only yield before you attack, you cannot yield after attacking. There is a relatively large gap of time before your attack. This is when you can yield.