Build Levels Easily
First, go to an area with a treasure box containing a star. Make sure you save somewhere close to the area. Now, get the star and hit as many enemies as you can. Then, die in battle and you return to where you saved with all your EXP! You can repeat the trick until you get your levels to where you want them.
Credit goes to: http://www.rpgclassics.com/shrines/snes/smrpg/secrets.shtml