…is the terracotta pot.
Don’t even think about planting them in pots without drainage holes, or pots that are glazed, because they can retain water that makes the roots constantly wet, which echeveria don’t like.
Another tip I’ve picked up is to mix the soil with perlite, about a 50/50 blend. Perlite is super useful at keeping the soil airy and light, and drains water really easily. The downside is that when you have a well-draining soil, you do need to water more often, and contrary to popular belief succulents do LOVE water.
If you have a large pot, you can pack in styrofoam or large pebbles at the base to ensure even better water draining. Styrofoam is useful for large pots because it allows you to keep the pot light while also providing useful drainage at the base.