Bit too long to make a guide for on this site, but I recommend the FFX-2 PC 100% speedrun guide availiable on speedrun.com. You can just ignore the fight strategies and it will summarize the key things you need to do for 100% completion without the fluff. 100% completion is not as intimidating and hard as it sounds and a lot of early GameFAQs guides are fraught with excessive anxiety and superstitions about what it takes to achieve.
And even if you DO mess up, its not hard to rush to Chapter 2, side with New Yevon and get the up to 5% extra completion you can get just for seeing those exclusive scenes.