Nice and Easy
 
Shuffle deck. Let someone choose any card, memorise it and
place on TOP of deck. Behind your back, flip THAT first card over
and bring out the whole deck.
 
Hold deck upright, so they see
bottom card - don't let them see theirs. With the bottom of the
deck showing, ask if that's their card, to which they say no. At
the same time you can see what THEIR card is, because you've
flipped it over and it's now facing you! Put deck behind your back
(be careful they don't see.)
 
Flip their card over again and put it
anywhere in deck. Bring out the deck, shuffle it or get them to
shuffle, and now you can find their card!