I am going to try all the sidequests to see if I can power myself up to beat Sin, I am trying to break the damage so that I can beat Sin easier. It is going to take me hours and hours but I am going to try and see if I can find a way to beat Sin. Even my younger cousin has yet to beat the game and he had it for ten years (he moved on to other things so that is another story), I am reading various guides on how to get the Celestial weapons and stuff but what else should I look out for before I beat the Final Boss?
Well, I would say learning Haste and Hastaga for Tidus and Rikku (everyone really), and Cheer! With this combination, bosses and fighting becomes very easy. Cast haste on someone with cheer and then use cheer at its max (I think about 15 times?). This, coupled with haste, will increase your strength by a LOT. This doesn't stick after battle, but it is very useful if you aren't looking for a three hit kill system, aka something challenging.