I would have written a quick guide myself, but there are already a couple of people that have done so, and probably did a better job at it than I would have been able to.
They both cover the same things and for most of the cards these guides will help you determine if you have a Wave 1 or Wave 2 card on your hands.
First one is from Stephen Bongner. He is the Administrator of the FFTCG Marketplace on Facebook. Plenty of knowledge on the game and cards. He created the “Distinguishing Final Fantasy TCG Opus 1 Wave 1 from Future Waves” guide and you can find it here.
Second one is from Conkwe, who runs the FFTCG Boards. I have been going these boards for since Opus VI. Other than his guide on Wave 1 differences, he shares lists of Errata, Promo cards and Variants, and is always a good place to check out. His Wave 1 guide “Differences in Opus I Wave 1 Printing vs Later Waves” can be found here.
These 2 guides are a great place to start figuring out the differences. I hope you find these guides as helpful as I have found them.