Instructions
Place a capable fighter on each team. While all team members must be able to fight, having one character (like Locke or Edgar) who has strong attacks using only regular weapons will come in handy during battles. Depending on where you are in the game you will have a few characters who meet this description -- make sure they don't all end up on the same team.
Put a "healer" on each team. Healers may not be the best in hand-to-hand combat but they have the ability to heal the HP of the rest of your team. Certain characters also have the magical ability to bring other characters back from the dead. Having this character around will become increasingly helpful as you near the end of the game.
Place someone who has a strong magical attack ability. such as Terra, on your team. This character will be able to carry out ranged attacks. Magical attacks, coupled with physical attacks and a character who is constantly healing and reviving the others will create a well-rounded team that can successfully take down all enemies.