Hey fellow Final Fantasy X explorer! When it comes to sphere grid progression, always focus on unlocking key abilities for each character first before branching out. Prioritize HP, strength, defense, and agility nodes to improve overall combat effectiveness.

For side quests, don’t miss out on the Celestial Weapons and Aeons. They provide powerful advantages in battles against tough enemies. Also, make sure to complete the Monster Arena challenges for valuable rewards and to unlock even stronger foes.

As for character builds, consider specializing each character based on their strengths. For example, Tidus can excel in agility and speed, while Auron can focus on strength and defense. Experiment with different paths on the sphere grid to find the best combinations for your playstyle. Good luck on your journey through Spira!