Instructions
Include at least two party members who can use many weapons and armor. Locke and Celes can use the most weapons. Cyan and Shadow wield their own special weapons.
Include at least one party member who can use several spells. While all characters can learn spells through the espers, some learn them naturally through experience. Celes and Terra are the best spell-casters.
Know each character's special abilities and when they are best used. If you need to take out multiple monsters at once, include Edgar and equip him with his tools. Sabin and Cyan's special attacks are good for big single hits.
Use certain players for defense. Relm and Strago can use the Heal rods to recover your party's hit points in battle.
Adjust your strategy when your best characters aren't available. There are major points in the World of Balance when you don't have Terra or Celes, and Locke is likely the last one to return in the World of Chaos.
Use each character often enough to build experience evenly. Since you'll need almost all of them in the last stage, you shouldn't let any fall behind on levels and have weak links at the end.