Black Mages can be one of the most powerful job early on if raised right and have the right equipment. One combination players can try is equipping a Black Robe and having the S-Ability Turbo MP from the White Mage. Another idea would be to use the Magic Pow+ ability from the Alchemist. Different elemental rods will enhance the power of the spell (i.e. Flame Rod enhances Firaga).