Before instance variables, I suggest first have the deck ready.
Make a Sprite called "deck", and have four Animations in there, of Spades, Clubs, Hearts, Diamonds. Each of them should have 13 frames in total and have all the sprites (images) ready therin.
This will organize your deck in a way that later you can program it according to your potential game conveniently.
Picking random card is easy - You just need to pick random animation and random frame within a given range.