With no FMC type machine to do it for you:
Multiply height in 1000's ft to be lost by 3 and add on an allowance to slow down if appropriate (typically 10 miles to slow from 330kts to 210kts). Descend at Groundspeedx10/2 thousand ft/min.
eg. At FL340, need to be level at a VOR at FL100, G/S 460kts.
You will need (34-10)x3nm = 72nm @ 2300fpm
If you need to be at 210kts at the VOR then start at 82nm and if the G/S drops drops off adjust the RoD accordingly, eg 420kts needs 2100fpm.
Just idle the throttles at T/D and wind in the appropriate RoD in the V/S.
Works every time.