(1) Write bug/feature on card.
(2) Add estimate of effort to implement or fix.
(3) Sort in priority order (collaborate with the user here)
(4) Take card off the top and work on it. When complete, remove it from the stack.
There are some compatibility issues.
I like the 4x6 size cards. My friend says that you can write too much on a 4x6 card and prefers the 3x5 size. I sometimes work with a guy who likes the really big 5x7 cards ... but that's just wrong.