When uncoupling the rear trailer, which of these should be done first?

Uncouple rear trailer:
Park in a straight line on firm level ground.
Apply parking brakes so rig will not move.
Chock wheels of second trailer if it does not have spring brakes.
Lower landing gear of second semitrailer enough to remove some weight from dolly.
Close air shut-offs at rear of first semitrailer (and on dolly if so equipped).
Disconnect all dolly air and electric lines and secure them.
Release dolly brakes.
Release converter dolly fifth wheel latch.
Slowly pull tractor, first semi-trailer and dolly forward to pull dolly out from under rear semi-trailer.