One of the easiest ways to keep a species going is to continuously propagating them.
I use this method, it is slow but a sure success.
Sometimes cuttings tends to dry up or rot
but these leaf propagation seemed to face better success rate than cuttings.
Here are the progress growth pictures in duration within few weeks.
Method:
A pot of sand, watering once a week.
Keep in a bright shaded area without any disturbance.
And they happily grow nicely.
Note:
Watering - just barely making the surface wet.
The sand should had dried off within few days.
Not to water until the soil is bone dry.
Here are Succulents:
Ghost plant
Panda plant
Donkey's Tail
and Mother of Millions (dark spotted leaves)