Here are a few of my tips.
- Remember as jaydinho is saying, only flick with your index finger. The middle and ring finger does not move!
- I find that you get a better shot if you mainly contract the card with the nails of your index and ring finger.
- The middle, ring and index fingers should not be touching eachother. I have found that this move is very easy if the fingers are relatively far apart. Not too much, but just so they don't touch + a little more then that.
- To get a higher shot remember to move your wrist upwards as you shoot.
- Catching the card is nothing but practice.