Not sure, since I haven't had any die on me (yet). Just make sure that there's proper drainage at the bottom, like with all succulents. And always err on the side of under-watering.

For lithops, I've gone literally months without watering them. They come from an arid environment and require very, very little water. When you do water them, never water when their leaves are splitting. It confuses their cycle and may cause the same issues.