I will edit opening post but I think also luck should be gained primarily from achievements. Every achievement point we get is one luck. Each luck is .005% chance extra for that drop rate or whatever it is (changes depending on what it is, whether it be crafting, gathering, atma farming, etc). That means every time you get an achievement for 5 points, you get .025% chance. In the long run this will be very helpful. Now apply gear which can be obtained via GC: another 50-100 points. .25-.5% chance. With 300 achievement points, 100 from gear, you have 400 points. That's an entire 2% chance which is HUGE now eat food which can increase your luck by 20%. You just got an extra 80 points. Pop that potion and hope for the best and voila. Now add materia for another 30-50 points and YEAH