The AFMs commonly specify the sequence of mags off, throttle to idle, mixture off, fuel selector off.
My inclination would be the reverse as fuel selector off halts the supply of fuel. Mags left on should get rid of the fuel in front of the firewall in the most acceptable manner.
Throttle to idle and mixture off before fuel selector off would trap the fuel in the firewall forward fuel system where there is most likely a leak
Discuss.