Take the cards out before your opponent arrives.
Determine the cards of value to you. These will be the highest-valued cards within the yu-gi-oh deck. (If you are playing a different card game, then these are the high-valued cards for that deck.)
Bend the corner to that card ever so slightly. Remember it cannot be overtly detectable to the human eye. It must be a bend that only you can notice without getting caught.
Wait for your opponent to arrive. Place the cards back in the packaging to remove any suspicion they may have about you and your antics.
Cut the deck in front of your friend. Whether in fourths, fifths or sixths, make sure you cut the deck with your desired card on the top of the pile. (Look for the bend.)
Re-assemble the deck of cards so that your friend does not suspect a thing. Also, make sure your desired card (the bent card) is on top.
Request that you make the first move. Otherwise, your friend will get the good card.