Preposition for Yoga Nidra is Shavasana, which is as follows

• Lie down on your back on the Carpet.

• Spread your legs at about 1 to 1.5 feet
  apart with toes facing outwards.

• Move your palms 3 to 4 inches away
  from the waist.

• Keep the fingers partially closed with
  palms facing upwards.

• Turn your head to any suitable direction.