Tips and tricks here don't affect your overall gameplay and achievements, but it's good to know if you are a diehard fan of FFIV.

• Golden rule: always use Slow, Haste, Shell, Protect, and Cry whenever you fight bosses.
• when you purchase items/equipment, you'll get a discount when you buy 4 or more, the discount apply to every 4 items. 
• You can use Left/Right buttons to de/select items by 10 when buying/selling.
• Bows and whips deal the same damage from both front and back row. that's why you should always put Rosa and Rydia at the back row.
• Staves and rods can be used as items to cast spells with the cost of 0 MP, sweet, isn't it? For example, when equip with Ice Rod, go to Ability, select any slot, select items, select Ice Rod.
• When casting magics that cause damage/heals to all targets, its effectiveness is halved. this applies to both White and Black magic. 
• Ninjutsu elemental attacks can pierce through Reflect.
• Crystal Mail is the only item that prevents Berserk.
• Break (black magic) is very effective against high HP monsters like Orges and Golems, it instantly KO them with 100% accuracy, so make sure to take advantage of that. It's available when Tellah and Rydia rejoin the party, and Fusoya.
• You can move items/abilities around by holding X button then drag it to a new location.