Also, to make the end of the game UBER-easy.
When you get to Ulti's Castle, and can be in a party without Squall, leave him behind at all times, and level up all your other characters (you could also work on this in the Deling City sewers with Quistis, Selphie and Zell, or in the missle base with Selphie and two others). Since the monsters' level is based on Squall's level, NOT the average party level, all of the fights in the final dungeon will be super easy. Unfortuneately, as the monsters' levels are based on Squalls, after a while your characters will not get very much XP for defeating them. I've never tried this scenario in the game, so I don't know how well it would work, but I can't see anything wrong with it, except that last point. Perhaps you could try leveling up at the Island Closest to Heaven/Hell, where everything is level 100. Or, spam Level Up on everything you meet.