Nothing easy. Fist step is to raise the strength of the character using Morph to 255. With this Cloud will be doing over 1500 with Ultima Weapon IIRC. After that if you still want more you are looking at using either Vincent or Barret. Barret's Missing Score gets more powerful with the more AP of the materia you have equipped on it, so you can generate a ridiculous amount of power, if you have the materia to back it up.

Vincent's Death Penalty has damage that increases with the amount of enemies he has killed. So if you put in the time to kill enough enemies you can theoretically deal 9999 damage with morph. (If you kill enough enemies you actually gain enough attack power it breaks the game and then enemies just automatically die. Even Emerald/Ruby Weapon.) Don't get your hopes up, we are talking over 65,000 kills.

All told most of these aren't particularly easy to do.