Lemme help ya buddy.

You might want to get the Caladbolg and Nirvana. I'm also working on the Godhand (which means I have to work on increasing the Strentgh of weak little Rikku) but those two should be enough. There is an Ultimate Weapon and Aeon Walkthrough up at the top of this forum. Use it to help you get these weapons. They're the easy ones (if you have the patience and luck for the Chocobo race that is).

Then, go to the map and search in the Bikanel Desert for a location called 'Sanubia Sands'. In here, you'll find Tidus' Ascalon. This swordhas no abilities except for Double AP. Very useful.

Anyway, after that is done, go to the ship and search the map for Omega Ruins. They're on the Eastern edge of the world, on a thin peninsula, with many clouds. Fight in here, but stay by the entrance so you may save after each battle. This way, if you meet a Great Malboro (and you will) and he kills you (which he almost always will) you won't lose any of your hard-earned AP. You may use the Caladbolg to kill fast, or the Ascalon to level up fast. I always go with the Ascalon, since Lulu's Doublecast Flare + Magic+10% + Magic+5% + Magic Booster + One MP Cost + Magic Power of 90 = 9999 + 9999 every turn for 4 MP combo can easily make up for Tidus' lack of Strength.