Summarize this article in one sentence.
Get a good grip on the card so you can hold it in place when it comes time to use the sleight of hand that makes it appear to vanish. Use your thumb and middle finger to grip about 1⁄4 inch (0.64 cm) from the bottom edge of the card. Hold the card firmly, but not so tight that it looks rigid and doesn’t move.

Summary:
Hold the card between your thumb and middle finger.