For sphere grid uberization: consult gamefaqs. BEATUIFUL guide on there.

else- save all your spheres you get of this nature: stat+ and fortune spheres.

break open all locks you are able.

acquire a healthy obsession with the monster arena.

sell superfluous weapons for Gil.

refer back to gamefaqs for an excellent method of systematically slaughtering the species bosses in the monster arena.

make everyone as good as you can. start with three people, let two or three go to waste, and slowly take a fourth character along the grid.

waste every non+4 sphere with a clear sphere.

get some overdrive->ap weapons and go huddle in fear while cactuar devours you. keep autolife running and overdrive=comrade (or stoic, but comrade has a slight more chance of happening seeing how you can control who cactuar counterattacks to)