Rule of thumb
When flying a 3 degree glideslope, the target rate of decent is 50% of ground speed times 10. For example: 90Kts GS / half = 45 x 10 = 450 fpm. Take the GS by half and add a zero is the easy way to think of it.
This will get you very close to dead on target.
Another rule of thumb: If you are all thumbs that day, it is a bad day to fly!