Woohoo! I love these guys. My Horatio has been plugging along for 5 years now.
But I digress... Here are some things that I've lived by for the past few years of crab-parenting:
+ People are very correct about the deep substrate. They like to have it deep enough to comfortably and securely molt. I like sand. It's vastly preferred and recommended over anything else. Just be cautious about the kind you use. Always research appropriate hermit crab sand types, as some sand out there contains additives that will harm or kill your crab.
+ Heat and humidity are key. Without correct humidity, their little gills will dry up and they will die.
I keep a thermometer AND humidity gauge in the tank as well as the special heater. The humidity gauge marks the appropriate humidity range for me so I know where it's supposed to be at. I'm not sure why, but I see people recommending that the sand be dry. It should be wet. If you can make a sandcastle out of the sand, and your crabitat smells like dirt, you're doing it right.
+ Water. I keep TWO water dishes out. Not too deep. One of (treated) freshwater with some flat marbles on the bottom to prevent drowning. And another of saltwater with a sponge in it to disperse the water and create the correct humidity. As for food, there are obviously special hermit crab foods. I recommend these as they (should) contain the oils that are so essential to crab diets. You can supplement it with pretty much anything. They're clawed garbage disposals.
+ My crabitat is a regular gymnasium. I keep a clear strip of sand in the front of the tank so that Horatio can have a place to scurry and run. And scurry he does! The rest of the tank is climbable aquarium decor, etc. They like to climb.