How to False Shuffle. False shuffling can be used to keep a card where you want it - on the top or bottom, third card down, etc.
False Dovetail Shuffle
Divide the deck in half and riffle the cards at the ends to mix them when using the most common false-shuffling technique - the dovetail.
To keep the top card in place, simply shuffle normally, but make sure that the last card to fall is your top card. If several of the top cards need to stay in place, make sure that the upper half of the cut deck is larger than the lower. The bottom half will finish riffling before getting to the cards at the top of the upper half.
To keep bottom cards in place, let them fall first, leading the shuffle.
Combine these techniques to keep top and bottom cards in place.
To do a completely fake shuffle, make sure that the upper half of the deck is smaller than the lower half.
Begin riffling with the larger half. You will do a real shuffle, but only on the very corners of the cards. End with cards from the smaller half on top.
Bring your fingers together as if you are finishing the shuffle.
Press down slightly with the hand holding the larger half of the deck. The corners should come undone. Do this while moving your hands together as if finishing the shuffle. Slide the upper half back on top.
Practice this move over and over again to be convincing. Once you get the hang of it, even someone watching closely won't be able to tell.
False Overhand Shuffle
Hold the deck in one hand. Pull up the cards and randomly drop them back in with the other when using the false overhand shuffle.
Hold the deck on its side in your left hand, fingers curled around the side and your thumb supporting the center of the deck.
Have the cards facing your thumb if you want to retain the top card. Have the pack facing your fingertips if you want to retain a bottom card. The key to this trick is to have the fingertips of your left hand keep contact with the card you want to retain.
Keep your body turned just slightly to the left so that no one can see you aren't shuffling that particular card.
Pull the cards up from the middle of the deck with your right hand, pressing slightly with your thumb to move a few of the thumb-side cards to the finger side. The card you want to keep should not move.
Shuffle the cards from your right hand into your left hand and repeat the action until you're satisfied. The card touching your fingertips is the card you wanted to keep in place.
The key to pulling any sleight-of-hand trick off is practicing it so that the motion is smooth, quick and natural. Any dovetail shuffle, fake or not, works better when the inner corners of the cards are used instead of the entire ends. Distract your audience by chatting. They can see you are shuffling, which is typically viewed as the setup to the actual trick, and generally won't pay much attention to your hands. You can use this to your advantage by setting up your trick right under their noses.