If you've ever watched a sleight-of-hand expert at work, you've probably seen them do this trick at least once or twice. Your expert takes a coin and, almost too fast to see with the naked eye, flips it down across and around their knuckles until it gets to their pinkie1. Guys in old gangster movies might also be seen doing this.
Impressive? Not really. Being able to perform this minor feat of dexterity takes more practice than talent. The secret to making it look good is to rely on gravity to move the coin across your fingers, and be confident enough to catch the coin on the way down.
The first step in training your hand to do this is to get used to the finger motions involved. The easiest way is to use a pencil, pen, or a similar object.
Hold the pencil between your index and middle fingers like a cigarette, somewhere near the middle of your fingers.
Now flip the pencil around and over your middle finger, so you can catch it with your ring finger. You should now be holding the pencil between your ring and middle fingers in the same fashion you were just holding it previously.
Repeat the rotating, so that you're now holding it with your pinkie and ring finger2.
Once you have mastered that, you can move on. Now, instead of using a pencil, use a coin. American quarters3 work well, but any coin that you're comfortable with will do. The choice depends on the size of your hands, the suppleness of your fingers, and how much you can afford to invest in coins that roll away, never to be seen again. Do the same flipping motions with the coin as with the pencil. This may be a bit more difficult, and may require using your thumb to help at first.
Once you have mastered flipping a coin with your fingers, you can try rolling it nearer to your knuckles. Here is the tricky part; the secret, as stated above, is to let gravity do the work, and use your fingers just to catch the coin and flip it over towards the next knuckle. When the coin gets to your pinkie let it slide through to under your fingers (or inside your hand) and use your thumb to push it back up to your index finger. Try not to worry about dropping the coin, as that will happen numerous times. In fact, if you keep a loose hold on the coin, instead of trying to guide it through every millimetre of movement, the flipping action will become much easier.
An easy way to practice is over a soft surface, like a bed or a desk with some papers on it. The shock absorbing surface will tend to prevent the coin from bouncing or rolling away. Also, a coin falling on paper makes much less noise than one falling onto a hard surface; which is an important consideration, if you are supposed to be busy doing something else.