We blow it by over-watering, not allowing for drainage and then these guys that are used to getting dried out from time to time, get mushy, sick and may die.
Here's my formula for healthy soil and happy succulents.
1- Choose a great well draining cactus soil. Many specialty nurseries offer a better drainage version than pre-packaged varieties in big box stores. But definitely don't use standard potting soil
2- Cut a small piece of screen material and place in the base of your container, over the drainage hole. This will stop ants from getting in and spreading disease.
3- Then add a pottery chip over the drainage hole to again help with drainage.
4- A secret I learned to help even more is sand on top of the cactus soil. Use 2/3 cactus soil in your container. Then top it off with 1/3 sand. This will allow the water to trickle down and not drench your plant.
5- Top off your cactus/succulent container with stones, glass, whatever you like for mulch and artistic appeal. My personal favorite is sky blue/white, almost glacier like recycled glass chips.
6-Try for a fresh, cool look - like adding jewelry or bling to your container garden design! And it's a surprising contrast with heat loving plants like aloe, echeverias, and agaves.
7- Remember succulents are drought tolerant and when in doubt, think drought-less watering is more and let them dry out in between watering - no more than 1 x a week.