To get easy experience, first beat the game with a level 10 character. Now you will unlock the cheatcodes and the Palantir of Sauron level. Pick a character and start the level. Immediately pause the game and enter the invulnerability and perfect mode codes. (the combinations are in the Secret codes menu in the level select screen) Fight your way through and see the experience rack up. You can get from level 1 to 11 in the initial fights, and the bonus points you get will get you to level 12. It takes 20-25 minutes per character to do this.