This is a fairly simple minded trick that still manages to fool most people.
Take a deck of cards and notice what one of them is and pull it back as you present the deck to someone. Suppose the card you know is the six of hearts. Tell the person to choose a card without looking at it. Announce that the card is the six of hearts. You look at it and say that it is correct and put the card aside. The card is actually the queen of diamonds.
Tell the person to choose another card without looking at it and say that it will be the queen of diamonds. You look at it and say that you were correct and place the card on the side. The card is really the eight of clubs. Finally you say that you will pick the eight of clubs. You now take the palmed six of hearts and put it aside.
Shuffle the 3 cards and then show them.