The Sphere Grid is where you develop your characters, increase their stats and help them gain new abilities for use in battle. The Final Fantasy Wikia site has a well designed diagram of the Sphere Grid which you can access by clicking here.
Below I will provide an outline of some of the more beneficial spells, abilities, specials and skills and show exactly where to find them on the Sphere Grid. Use the links below to jump to a specific section if you would like more information:
A key skill found in Auron’s section of the Sphere Grid. This ability drops an enemy’s defense down to 0 and removed the Armored status. This ability is pretty much a requirement for some of the fights in the game so it is important that you have Auron obtain it and have one of your other characters learn it using a Skill Sphere if you don’t plan on using Auron.
A white magic spell available in the early portions of Yuna’s Sphere Grid that requires a Lv. 4 Key Sphere and a Lv. 1 Key Sphere to reach. Auto-Life instantly revives a character with 25% HP.
A black magic spell found in Lulu’s section of the Sphere Grid. Bio causes Poison which will inflict damage to an enemy each time their turn comes up. It is incredibly useful against enemies with a high amount of HP.
A special ability found at the start of Tidus’ area in the Sphere Grid and one of the first moves that he will learn. Cheer raises each characters strength by 1 point each time you cast it up to a maximum of 5 times. It also raises each party member’s defense stat.
A white magic spell at the beginning of Yuna’s section of the Sphere Grid. This spell is used to remove any negative status effects from a party member. You should still have Yuna learn the spell so that another character can copy it from her if you do not plan to use her in your party.
A special ability found in Lulu’s area of the Sphere Grid. Focus raises each party members Magic stat by 1 point each time you use it up to a maximum of 5. This is a great boost to use on Lulu or Yuna. It also raises each character’s Magic Defense stat.
A key skill found at the end of Auron’s section of the Sphere Grid. This ability has a huge MP cost associated with it but it inflicts Power Break, Armor Break, Magic Break and Mental Break on the enemy at the same time. It can be extremely beneficial for some fights.
A key white magic spell available at the beginning of Tidus’ section of the Sphere Grid. This is an incredibly useful and highly utilized spell. It increases a characters Agility stat allowing them to have more turns in battle.
A key white magic spell available at the end of Tidus’ section of the Sphere Grid. This is an incredibly useful and highly utilized spell just like Haste but it is automatically applied to all party members when used.
A key white magic spell available at the end of Yuna’s Sphere Grid. It can also be picked up by Rikku if you use Key Spheres to unlock an extra pathway. Holy is a very strong magic (holy-type) that does a lot of damage to enemies but takes a lot of MP to cast.
A special ability found in Kimahri’s section of the Sphere Grid. It absorbs an enemies HP and MP. When Kimahri uses this ability on an enemy he has a chance at absorbing one of the enemies abilities and learning a new Ronso Rage ability (check out the Overdrive section for more information).
A special ability found in Rikku’s section of the Sphere Grid. Each time you use Luck it will increase each party member’s accuracy and chance of landing a critical hit. It can be used up to 5 times.
A skill found in Rikku’s section of the Sphere grid. This skill allows the character to attack and steal from an opponent at the same time. It is incredibly useful and you should make sure to go for it as soon as possible. This is a great way to keep your important items stocked (X-Potions, Mega Potions, Phoenix Downs, etc.) and to find items so that you can customize your armor. Rikku does not have many moves that require MP so you should be able to use Mug during nearly all fights.
A skill found in Auron’s section of the Sphere Grid and one of the first abilities that Auron will obtain. Power Break reduces an enemy’s Strength stat down to 0. This can be helpful against enemies with strong regular attacks.
A skill found at the end of Tidus’ section of the Sphere Grid. This move costs a significant amount of MP but greatly reduces the recovery time of an attack so that you can get more regular attacks into a fight before your opponent’s turn comes up.
A white magic spell in Yuna’s section of the Sphere Grid. Once Regen is cast on a party member they will regain a portion of their HP each turn. Regen is added as a side effect of some of Rikku’s Overdrive moves.
A white magic spell available near the starting point of Kimahri’s Sphere Grid. You have to circle around Ultima in order to obtain it. The need for this spell is negated by any weapon that has the Sensor auto-ability.
A special ability found in Rikku’s area of the Sphere Grid. Items can be stolen from nearly every fiend and boss in the game. This move can essentially be replaced once you reach the Mug ability (which allows the character to simultaneously attack and steal items).
A special ability found in Rikku’s section of the Sphere Grid. This command allows Rikku to use certain items in the middle of battle. The most important of these items are Al Bhed Potions which essentially allow Rikku to act as a secondary healer in your party.