Good Nutrition
Animals should have ready access to fresh water and the proper nutrition for their species. This aims to maintain their overall health and minimize thirst and hunger. Just like humans, animals can become deficient in vitamins and mineral and that can lead to weakened immune systems, obesity, malnourishment, and other health problems.
Good Environment
Provide sheltered areas to protect the animal from heat, sun, and fear. This isn't just about being able to hide. Air quality, surfaces to rest on comfortably, and proper temperatures are also important to maintain. Enclosures need to be properly ventilated.
Good Health
Prevent or rapidly diagnose and treat illnesses and injuries. You should also be providing ways to support proper muscle tone and cardio and respiratory function. Proper humidity levels can prevent respiratory infections in reptiles. Illnesses are stressful on everything, not just people!
Natural Behavior
Provide sufficient space, proper facilities and appropriately varied conditions. Reptiles are tame, but in many cases, they are not domesticated. Bearded dragons, crested geckos, ball pythons and leopard geckos are known exceptions to domestication. Provide climbing space for arboreal and semi-arboreal animals. Provide deep substrate for animals that burrow. Provide basking areas for animals that bask.
Good mental Health
Provide species appropriate opportunities to facilitate positive experiences. Sometimes enrichment is a learning opportunity. If you have a bearded dragon climbing on a jungle gym designed for reptiles and he falls, he can navigate getting back up. Supervised enrichment will allow you to intervene if necessary. Knowing things like that will help when setting up your enclosures.
These are basic provisions any animal should be afforded. All animals, from dogs and cats to fish and spider and bugs, should have clean water and food that is not spoiled. All animals, from reptiles and amphibians to livestock, should have access to shelter.