I have several succulents, a couple that are doing well and a couple that are not. I have an aloe that is doing great. I haven't watered it in months and it keeps growing. I don't understand that, but I'll take it. Then I have some that are not doing well. The main stems keep dying and I have to pull off the branches that are still alive and try to root them. I have a crassula and a burro tail. Last winter I had the same thing happen to a Kalanchoe. I've tried to only water them when they start looking wrinkled. The crassula has been looking wrinkled for a long time and watering it did no good. Since it cooled down a month ago, I started putting it outside. I think the stem was already dying, I just hadn't noticed until I brought it back in a couple of weeks ago. Over the summer I had a bad gnat problem, but fixed that with some sand. The aloe escaped the gnats as it was in another room. When I pulled off the remaining branches of the crassula, I also pulled the dead stem. As you can see from the picture, there are no roots on it. The burro's tail is down to just a few shoots. It has been dropping leaves for months and I've tried watering more, watering less, more light, less light. I think it's one step away from the compost pile. Both are mostly indoor plants. Last winter I kept the crassula outside except for frost nights and it was doing great. I have no idea what I'm doing wrong.
I think that once they start to shrivel the root system is shot for the most part. The trick is to water regularly so the roots stay alive but not so much you cause rot. How much that is depends on the light, temperature, time of year and the kind of plant. So you have to research each species and figure out what combo of these factors along with the right amount of water will work for the plant.
Take heart , over time you will get better and have more success.
Many types of crassula do NOT do well here in Arizona. They need cooler nights and higher humidity than we can provide in Arizona. I know you had them inside but, plants know where they are! I grew beautiful crassulas when I lived in the East and also in California. The same goes for burro tail. It tends to drop all its leaves here. You find these plants for sale here, especially at places like HD, Lowe's, etc. that come from CA and look wonderful, but are not successful here in the desert of Phoenix. You are on the right track with aloes that, for the most part, do very well here. If you like to grow cacti & succulents, I would recommend Miles Anderson's book The Complete Illustrated Guide to Growing Cacti & Succulents. He is located down in Tucson and sells plants that grow well in this area. He also tells you which ones do well as indoor houseplants here.
Most succulents slow down in growth during fall and prepare for a dormant period even in warmer climates. It is the amount of daylight and longer night that triggers it. When a plant is dormant, it doesn't need the same amount of moisture as it does when in active growth. Burro Tail is one such plant.
When a plant goes too long without moisture, the soil dries and shrinks away from the side of the pot. When you water, it doesn't wet the soil ball but runs out through the sides. The trick is to place the pot in a saucer full of water and sprinkle some on top to strart the syphoning up from the bottom.
Too long without water, the roots die and so the plant becomes overwatered since it can't use all the water given.
As Colleen stated, I think you're keeping your succulents too dry. Are you growing the succulents indoors or outdoors?
If indoors, the plants will need water regularly, allowing them to dry somewhat between waterings. Water well when you do water and then let them dry, but not completely, before you water again.
Depending on the soil the plants are growing in, if there is quite a bit of peat in the soil (as there often is when plants are grown in a nursery) the peat will pull away from the sides of the pot as it dries and you will need to soak the pot in a pail of warm water to get the soil mix to become moist again. Just watering from the top of the soil doesn't really do anything since the water just runs down the side of the pot where the soil pulled away from the pot.
Even though succulents are adapted to growing in dryer than normal conditions, it is never quite as dry in nature as you might think. Succulents are able to absorb moisture from the dew that forms every night and even though they are not getting rain, they are still getting some moisture every day. A plant will get dryer growing in your living room than it would ever get growing outside.
If I buy a potted succulent, I always repot the succulent into my soil mix to make watering easier. With my mix, I know how fast the mix dries out, so I can judge when the plants need to be watered again. If plants are left in the soil they were purchased in, you will have just about as many different soil mixes as you have plants - and that can make watering correctly very difficult.