Well from what i have learned from my instructor , if u need to reach a particular point at a certain height ( with regards to jet aircraft ) , then " Descent point at which the descent must be initiated is three times the altitude " , meaning from FL400 to ground level , u would need to start your descent at 40*3=120 nm out and rod should be 1000 fpm or greater.It works like a charm for my beechjet.I have found this to be the most simple way of flying the descent.
Regards
Skyking
