Have a look at the version in Vol 3 of the Tarbell series, p. 284. It's very good. You need to play with it a bit to work out the handling.
A few subtleties to consider: camouflage the card by using a part of the paper that has an easily recognizable photo or design; do it blindfolded, using the commonly understood technique; get an assistant to have someone take the card; use a large knife that is easily seen; do not stab the paper repeatedly -- move the knife slowly over the paper, then plunge it into the card; have the assistant slowly tear away the paper and dramatically raise the knife to reveal the card.
Done this way, it has a powerful effect that people remember.