Achievements
Many of these Achievements can only be unlocked while playing the Encore and due to many being story related, SPOILERS may ensue. There are 22 achievements worth 1000G and all are secret.
Claves's Resurrection (50G) - Collect all 7 pieces of Claves's Soul.
EZI Worshipper (321G) - Collect all EZI items in the game.
Fantaisie Impromptu (10G) - Complete chapter 3.
Grand Finale (70G) - Defeat Frederic with Claves unlocked.
Grande Valse Brilliante (10G) - Complete chapter 4.
Heaven's Mirror (10G) - Complete Final chapter: Heaven's Mirror.
Hero's Gate (30G) - Use the Hero's Crest to open the way to Mysterious Unison.
Heroic (10G) - Complete chapter 7.
Nocturne (10G) - Complete chapter 5.
Party Level 2 (10G) - Obtain party level 2.
Party Level 3 (10G) - Obtain party level 3.
Party Level 4 (10G) - Obtain party level 4.
Party Level 5 (10G) - Obtain party level 5.
Party Level 6 (20G) - Obtain party level 6.
Pirate's Treasure (80G) - Finally obtain Dolce's treasure.
Raindrops (10G) - Complete chapter 1.
Revolution (10G) - Complete chapter 2.
Rondo's Return (50G) - Defeat Rondo in Mysterious Unison.
Score Piece Collector (100G) - Collect all 32 Score Pieces.
Soul Released (79G) - Free Chord's Soul from Fort Fermata.
Tristesse (10G) - Complete Chapter 6.
Xylophone Treasure (80G) - Use your orb to open the secret door in Xylophone Tower.
New Game+
Complete the game once and save the data when prompted to. Then load the game to begin a new game with all obtained Score Pieces, Party Levels and a Hero's Crest. Plus, the enemies and bosses will be much stronger and tougher in battle.
Echo Meter
Be sure to build up your Echo Meter during each battle so that you can unleash your special attacks with more damage. You build the meter by attacking enemies with your regular attacks, which will build it up to 4 hits, 8 hits, 12 hits, 16 hits, 24 hits, and 32 hits (the latter being the highest). Unleashing special attacks at that plateau will result in the most powerful attacks your characters can use, but be sure to use them in the present battle, because the meter, even if unused, will be reset before the next battle.
Pictures
If you're in need of money, remember that you can take pictures with Beat's special skills and sell them to vendors. Pictures of enemies and especially bosses are valuable and can net you lots of cash.