start from a hip carry (see 'hip carry' instructions). have the rings higher on your shoulder than normal.
lift your child's weight with the arm opposite the rings. use the other hand to pull the rings around as you shift the child to your back.
leaning forward to adjust can be helpful...
now tighten the rings and if you choose you can wrap the tail around the rings in a sort of a knot... now you are hands free!
(whenever you are doing a new carry have a spotter on hand to help assist you. a mirror can also be very helpful to get things just right)