I am gonna copy and paste what I just posted on NETPLAY GENERAL into here for future reference.
I posted a few ways on the Dissidia thread in Misc. Fighters. The AP way is there, PP... you can always set your day to your special day and play that way.. it really will just come to you.
For EXP... Best way is to jump on the black chocobo play plan... wait until you get a 5x bonus, save... then do a team versus the CPU. Select 5 easy characters to beat like Gabranth, Garland, Tidus, Emperor, or w/e you find easy yourself... Then choose 5 characters you want to level.. or 1 of your strong ones, and then 4 other characters you want to level. Load them all up with Chocobo feathers, wings, and all the EXP boosting accessories you have. Make sure you are on your special day(and again, that you have the EXP x5 bonus with the black chocobo active). Now, fight the team battle, beat 4 of them, and on the 5th guy, exit to your PSP's main menu. This way you can keep the chocobo x5 bonus and keep using that to level up everyone.
Oh yeah, make sure you have pruchased the PP Catalogue item for being able to set the level cap of your opponent to level 100.