In the early 1930s, the famed parapsychologist J.B. Rhine and a colleague, Karl Zener were using a standard deck of playing cards as a method of testing for both clairvoyance and telepathy. However, there were a couple of problems with this system...not only did a subject have to correctly name both the suit AND the number on the card, but it seemed as if people were more apt to pick their favorite suit, rather than truly put their clairvoyant skills to the test.
To combat these problems, Zener designed a new deck of cards to be used. This deck, consisting of five symbols, totaled 25 cards--five cards each for the five different "suits." The new symbols consisted of a circle, a cross, three wavy lines, a square, and a star.
Nevertheless, the Zener Card Method is still standard in preliminary ESP studies. According to the Null Hypothesis, the average person will have a 20% success rate, scoring one correct answer per 5. Rhine also discovered what he called the Decline Effect---success rates were higher during the first few times a person went through the test. After that, results became progressively worse with each additional attempt at the test.
To ensure the most accurate test results, it is recommended that the test subject and the person conducting the test have some type of barrier put between them, to ensure that the cards cannot be seen, and that no visual clues are being given. An objective third party, or videotape session can also improve integrity and ensure that no audio clues are given. In addition, to prevent the possibility of "card counting," the subject should not be told whether the answer given was correct or incorrect.
Zener cards can be easily purchased online, or made yourself, for your own experiments. There are also online tests available based on the Zener Card Method, which I've linked to below.
Zener Card Test