Make sure you are wearing a shirt/sweater with long sleeves. I cannot stress how important it is to have that. Choose a shirt/sweater with a fairly loose hanging sleeve. Not one that shrinks tight. Position your hand with a coin (penny preferably for it's weight) as shown.
Step 2: "MAGIC"
Snap your fingers over the selected coin, being sure to smack the coin into your sleeve with either your middle or index finger (whichever finger you use when snapping against your thumb)
Step 3: Smile
Wave your hands in a sparkling fashion, exclaiming how the coin has miraculously disappeared. Watch as expressions of awe and mystery stretch across your victims faces. Congratulations.