How do you plan the descent in emergency landing practice?

or too low. You have to rely on your altimeter and use several
'target' altitudes until you turn final.
I disagree. Of course the alitmeter can be very helpful, but only if you
know the ground elevation and if you are sure your current altimeter
setting is correct.

Correct. Additionally, altimeter will tend to stick with engine off.
Glider pilots are taught to ignore altimeter during circuit and
landing.

Bartek