Sounds like you are looking for advice more suited to a non-advanced play style (no insult intended -- there are just some things you can't do until after you beat Yunalesca, like go to the Omega Ruins...). If you can go back to the Sanubia desert -- and I'm not sure you can at your point in the game -- look around for Cactaurs. They give bunches of AP. My characters were getting 2 and 3 AP at a time for beating them. If you can't go back, hanging around the calm lands NW corner will get you some decent critters to raise your stats. You might also want to head back to Mt. Gagazet and Zanarkand ruins. (Have you been to the battle arena yet and bought the capture weapons? You can capture creatures for him as you gain levels...)

The ruins are also where you should be able to find a few level 3 and 4 key spheres. Not a ton, but a few. I only got three or four of each before getting control of the airship. Used them to unlock Ultima, Doublecast and Auto-life!