Damn, I wanted to be the first one to post.

There's not a whole lot I can say as FFIX is probably the easiest FF game I've played. One good thing to know from the beginning is to steal. You can get some good weapons early on the game by stealing from the first enemy. I'll try to event spoiling here and just basically tell you to steal from about every boss you encounter, except for the two you will fight in the forest since they won't give you anything special. You might get frustrated with a bit early in the game until you get the ability Bandit which increases your chances of stealing. Generally early on your chances of stealing the best items are based on luck.

In this game you learn abilities from equipping armor, weapons, and accessories. You can choose to leaves those equipments on until you've learned the ability or you can choose to just equip those items on when you need those abilities. Also use Focus with Vivi whenever you have the chance. It increases his Mag and I believe the effect stays on even if he's KO'd.