managed DES on the 330 ends up looking like ALT x 4, until 10'000.
i normally do 2 calculations. i do alt x 4 for managed des. comfort, no diving.
then i do alt x 3 + (1nm/10kts speed over green dot)+(+1nm/1kts tailwind or - 1nm/1kts heawind). the second calculation is for OP DES. no speed brakes.
below 10'000 i cross check dist to go x 3 is GS. if at green dot speed you should aim to be below GS by at least a thousand or more to start decelerating to configure.
if you are ON profile, and then you get vectors for short cut, your action should be as prompt as possible, speed brakes out ASAP(doesnt necessarily mean full brakes, could be quarter or half or anywhere in between). increasing speed depends on the situation (ATC restrictions, Dist to go).
the best is getting to know your destinations ARR proc. some places have a tendency to surprise you by cutting you short on the STAR. everyday! so once you know which ones cut you short, and normally where they cut you to (quick 10 mile final or direct to the FAP). so if flying in to these fields, always aim to be low, or ask for track miles to go when getting vectored.