Final Fantasy Tactics Advance Cheats

Secret Characters
Beat the game once and fulfill the following conditions, and the secret characters will offer to join you if you have space:

Shara - Clear "A Maiden's Cry" and enter a town.
Ritz - Clear "Mortal Snow".
Ezel - Choose "Gossip" at his shop, and then clear "Reconciliation".
Babus - Clear "Left Behind" and enter a town to enter "With Babus" mission. Clear it to get Babus.
Cid - Clear all 300 numbered missions. (Top secret missions do not count.)

Semi-Secret Characters
Semi-secret characters become available by completing a mission with different mission items. The secret characters might join your after the battle.

Cheney: Complete a mission with Snake Shield as a mission item.
Eldena: Complete a mission with Elda's Cup as a mission item.
Lini: Complete a mission with The Hero Gaol as a mission items.
Littlevili: Complete the "Clan League" mission.
Pallanza: Complete a mission with Wyrmstone as a mission item.

Extra Experience
If you ever run into a gel-type creature called a flan and need a little exp, here is a tip. First kill off every other enemy on the field, and then surround the flan with your people. Use regular attacks on it, which will only do 1 damage, and if the enemy is of sufficient level, you'll gain a few levels while slowly killing it.

Get Lots of Experience Points Early On
During Mission One, send all of your party members except Marche to the right to defeat the short enemies. Send Marche forward so he is in front of the sprite (the fairy-like creature). The sprite will do about 5 damage to Marche every turn. Marche can heal himself 7 points each turn, and he gets 10 EXP each time he does it. Keep having Marche heal himself over and over, and this way you can get him to a high level very early in the game. You can also have your other characters attack Marche, and they will gain a lot of EXP because Marche is at a much higher level than they are.

Getting Ribbons
Put 4 different towns around in a circle, so that they will surround a blank space in the middle. Then, put a Jagd in the middle. The treasure hunt at the Jagd will result in a Ribbon. (Ribbons can only be worn by Viera. They nullify ALL status ailments, including Doom.)

Hunter's Ultima Weapon
During the mission "over the hill" when you fight against Ritz and her clan, use a thief with the steal weapon ability to steal Shara's weapon, called SeventhHeaven. Equip it to a Hunter and it will learn Ultima Shot.

More Effective Treasure Hunts
The most effective Treasure Hunts are performed like this:

Best: Two of the same type of symbols (e.g. two forests) at the top of the circle and two of the same type of symbols (e.g. two mountains) placed on the bottom part of the circle on the world map, with another symbol in the middle (as the final symbol placed).
2nd Best: Four symbols in a circle with another placed in the middle (as the final symbol placed).
3rd best: Three symbols in a circle with another placed in the middle (as the final symbol placed).

Quick Reset
To reset while in the game, press A+B+START+SELECT.