Final Fantasy X Tips

easy training &more
It's simple actually. All you have to do is while in battle, make sure you switch through every character so that everybody can get points at the end of the battle. If a character really has no point during the battle, like before Yuna actually gets any damaging moves and besides healing there is really no point in using her (that's how they get behind the the characters and are weaker and you rarely use them) you can just press the triangle button, which makes them block, then switch them out during their next turn. Same thing goes for if you just switch to somebody and have them use an item.
So they don't actually have to deal damage, but they have to take some part in the battle. I've been doing this for a while, and it levels everybody up very quickly all together.

I like to do this with harder battles, or just for easy wins.
You switch through every character pressing triangle for everyone.Nobody deals damage, or does anything.Then I end up switching to Yuna, and summoning an aeon.
and some random tips about fighting with aeons, that you should pretty much know.

Certain aeons are immune to certain elements, like ifrit,ixion and shiva.
When you are fighting a fiend that casts fire, then you should summon ifrit because any fire dealt to this aeon, will only heal it. Even if you aren't fighting with a fiend that casts the element that it is immune to but you are using ifrit, and your hp starts to get low, cast fire (fira etc) on yourself to heal yourself. with ixion you would use thunder, and shiva blizzard etc That makes them last a little longer. of course later in the game you will be able to give them items to make them learn new abilities like curing, but this definitely works for when you don't have that.