Urdhava akinchasana (Day 77) is ideal preparation for this subroutine.
As with akunchasana use the fill length of the forearms to control your balance, especially the elbows.
Engage the bandhas especially, uddiyana (drawing in the belly) for lowering of the leg to the front.
Lower from the hip rather than from the foot
Stretch out through the length of the leg as you lower.
Stretch through the leg that remains vertical
Ideally the vertical leg should not come forward while the other leg is lowering, nor should the knee bend.
When lowering the leg to the side press down through the elbow on the opposite side to stay balanced
In viparita garandasana, begin to wrap the leg as low as possible,
Once wrapped stretch up though the leg that is being wrapped, try to stay straight and not lean backwards.
In the back arch, twist first and then arch the back.
Anchor the head and elbows as you twist
Press down firmly into the mat, the elbow on the opposite side to which your twisting.
Engage mula and uddiyana bandha to help support the arch of the back, engage the hips and push them forward.