Look up an explanation of what the numbers mean during the card game online somewhere. The game doesn't tell you at any point, making playing it incredibly frustrating (and the game forces you to play it at one point, so it's pretty important).

Other than that, I'd give you the same advice I'd give for most FF games! Steal as often as you can, and don't let an enemy die before you've stolen its items or at least detected what it has. Learn all the abilities you can. For end-game grinding, make sure all your characters equip the Reflect ability and go fight dragons on an island to the northeast of the world map. Also, make sure to run around in patches of woods that may be hard to reach, you'll often come across a special encounter!