Step 1: Preparation.
Hold your left hand with your fingers together and pointing to the right, thumb uppermost.
Fold your thumb ninety degrees at the knuckle so that it is pointing at your body.
Bend you right thumb at ninety degrees as well.
Lay your right thumb along the top of your left index finger, with both bent knuckles touching each other.
Roll right index finger around the two knuckles to hide the join.