You then have her go through the moves in the random order she mixed the cards in. Going forward, backwards, left and right as the cards tell her to. If she can't make a move because it would take her off the map, have her place that card on the bottom of the unused stack, and you'll come back around to it later in the procedure.
Eventually she'll land on one space on the map. You push the papers aside and draw her attention to where she ended up.
"Okay, your favorite kind is the pecan cluster, right? And you ended up right here... one up and one to the right of center. Open the box."
When she does, she finds that right in the location she landed on is her favorite piece.
"That wasn't a fluke. I'll show you," you say. "I'll move it to a different location." Behind the cover of the box you mix the chocolates around then cover them back up.
You tell her to pick up the direction slips up and mix them into a completely new order. This time you tell her to take one out at random, don't look at it, and put it in her pocket. She does.
You go through the process again with the coin and the map, moving around based on the slips of paper.
At the end of the procedure you have her remove the cover from the box and find out how close she was to her favorite piece. She's two pieces in front of it.
"But remember," you say, "You put one slip in your pocket without looking at it. Pull it out. What does it say?"
She pulls it out and it says, "Move 2 Spaces Backward," landing her right on her favorite piece.
The algorithm works!
Method
This is a good introductory effect to familiarize yourself with the Konami Code. Tomas has more complicated ways to hide the method, but it's best if you first understand what is going on.
Here's a PDF of the map, and here's a PDF of the move cards (to be cut out). You probably wouldn't use this exact layout, but you can practice with it and see how you can apply it to your own box of chocolates (or anything else in a grid).
Print the move cards, cut them out, and set the last two aside for now (1 to the right & 3 backward). Now put a coin in the middle, shuffle up the moves, and then go through them and see how it plays out. You will always end up one forward and one to the right of where you started, unless you screw it up, which I wouldn't put past you.
So, assuming you know what your friend or girlfriend/boyfriend or spouse's favorite type of chocolate is, you just put it in that location to start and you're good to go.
Before the next round you will place her target piece two to the right and two down from center. The diagram below indicates where the marker will wind up at the end of the first and second round.