I use as a guide the 3x profile.
The explanation is based on the aerodrome being at sea level. If you want to level off etc or aerodrome is higher, adjust.
Take a look at the altimeter. eg, 8000'.
To commence a descent on a calm day multiply 8 by 3.
That gives 24.
Therefore on a calm day to arrive at the aerodrome using a rough 3 deg slope, you'll need to commence your descent by 24 miles out.
How fast should you be descending? Monitor your distance versus height profile. eg, by 7000' you should be 21 miles from the aerodrome.
A good guide for your rate of descent is the same as the one you use for the ILS. Half the groundspeed X 10. eg 200kt g/s = 1000 fpm.
If you have nervous passengers and in an unpressurised aircraft, try a 5 x profile. The rate of descent will be less.