There’s a couple things you can do to save your plant.
- Soil: What kind of soil is in there? If you are using standard potting soil, you need to replace it. Potting soil is designed to hold on to moisture and usually is filled with fertilizer. Neither of these are good for your succulent. Any garden center should sell small bags of Cactus and Succulent mix. If not, or that’s not an option, find some sand and mix that with regular soil. It will increase drainage and reduce fertilizer density.
- Pot size: How long have you had the plant? It may be outgrowing the pot. When this happens, the roots can’t grow enough to support the needs of the new leaves. The plant will sacrifice healthy leaves to feed the rest of the plant. Succulents store water and nutrients in their leaves so they don’t starve during rough times.
- Watering: As pretty much everyone else said, you may be over watering your succulent. They need almost no water at all. The soil should be completely dry for at least a day before watering it again. Over watering can lead to rot caused by fungus or bacterial growth. You should remove any leaves that look rotten to avoid spreading. If rot has already reached the stem, you’ll want to pull off healthy leaves to propagate into a new plant.
- Light: When a succulent isn’t getting enough light, it will attempt to grow taller rapidly to try to find more light. When it does this, it again sacrifices the lower leaves and uses their nutrients for rapid growth. If your succulent seems to be growing on top but dying on the bottom, you may need to find a spot with more light. Be careful, though, you don’t want it to get too much direct sunlight. Dappled light is the best for them, but lots of shaded light will work well.