Tell someone that you are going to make the coin disappear.
Put the coin on a table, pick it up with your right hand and place it in your left hand, close your left hand, place you right hand on your neck behind your head, knock on your right elbow with your closed left hand, open your left hand and see the coin fall, say: "Sorry, it didn't work, let me try again".
Again, put the coin on the table, pick it up with your right hand and place it in your left hand, close your left hand, place you right hand on your neck behind your head, knock on your right elbow with your closed left hand, open your left hand and see the coin fall, say: "Sorry, again it didn't work, let me try one more time".
Put the coin on the table, pick it up with your right hand, simulate that you place it in your left hand, hide it in you right hand by closing the pinky and ring fingers over the coin, close your left hand, place you right hand on your neck behind your head, let the coin fall through your back inside your shirt, knock on your right elbow with your closed left hand, open your left hand and say: "See, I knew I could do it!".