I have at least played and beat the game one time but I can give you some pointers on how to progress your characters. You probably already know that whatever you do in battle determines the stats that go up in FFII. The best way to strengthen your characters is to (literally) have your characters attack themselves. Make sure you're fighting in an area with weaker monsters, make sure there is only one monster on the field, if there is more, kill the monsters until there is only 1 left, and attack your characters until your hp gets low and then kill off the monster and you'll gain stats quickly. Don't let your party's hp get low enough that the monster will finish them off. Repeat the process and you'll see your strength, defense, stamina, etc. raise rapidly.