1. Lie on your back in a comfortable area.
2. Place one of your hands over your eyes so you can't see.
3. Stick only your index finger (Pointing finger) up in the air with the hand that isn't covering your eyes
4. Think of a letter, number, or shape, but don't move your hand
5. Move your mouth in the direction you would start at, or imagine yourself drawing it with your fingure.

Remember: Don't move your finger/hand while you are doing this. Don't purposely keep it still, but instead don't control it.

Edit: I'll put in an example for the last step. If you are trying to do an uppercase P starting from the bottom, either imagine yourself drawing it, or move your lip upwards.

What's supposed to happen?

Your finger is supposed to move without you making it.