Hey fellow Final Fantasy X explorer! When it comes to sphere grid progression, make sure to focus on upgrading your characters’ key stats first, like HP, strength, defense, and magic. Use the expert sphere grid for more customization options.

For side quests, don’t miss out on the monster arena challenges for great rewards and tough battles. The celestial weapons and aeon battles are also worth the effort for powerful upgrades.

In terms of character builds, consider specializing each character in a specific role. For example, Tidus can be a fast physical attacker, Yuna a potent healer and summoner, and Lulu a black mage powerhouse. Experiment with different paths on the sphere grid to find what works best for your playstyle. Happy exploring!