Greek Shift Here we go: Control the card you want to force to the top ...
# Hold the deck face up in the right hand between the four fingers and the thumb. The four fingers are at the top edge of the cards ( the edge closest to the audience ) and the thumb is at the inner edge. Begin sliding cards of the top of the deck ( this is actually the bottom of the deck because it is turned over face up ) with your left thumb. This is basically a dragging action, as you drag the card to your left and the rest of the deck to your right. You are to show the spectators each card as it is slid off the pack. When you slide the selected card off the deck, get a little finger break underneath it.
# So now you have a few cards in your left hand with a little finger break under the top card and the rest of the pack in your other hand. When you move to slide the next card onto the small packet, the selected card ( held by the break ) is secretly added to the bottom of the deck ( which is actually the top). With practice, this becomes real easy to conceal the move.
# You must not hesitate or fumble. It must seem as if you are just sliding another card off the deck. From here you can continue to slide cards off until you reach a desired number of cards.