The large number of exotic species prevents us from going into much detail about the care and medical needs of each, but following general guidlines can be a good start if you find yourself drawn to the "out of the ordinary" type pet.
Knowledge: If you are keeping exotic species, including birds, snakes, reptiles, amphibians, sugar gliders and other marsupials, hedgehogs, guinea pigs, hampsters, gerbils, rabbits, etc. etc....you need to have a source for information on proper feeding, housing, and medical care. Many books are available, but the internet has become a valuable source of quality, up-to-date information as well. Just remember - just because it is on the internet doesn't make it true. Check the info you get from new sources against the other info available, and check the credentials of the person giving the information.
More exotics come to us with illness or injury due to a lack of proper housing or husbandry than any other cause. Calcium deficiency in iguanas and sugar gliders, too much fat in bird diets, parasites on hedgehogs, teeth problems in rabbits and rodents due to lack of chewing material, and skin problems due to the wrong humidity, overheated hot rocks or lamps, or dirty conditions in reptiles all come to mind. Finding good souces of information on a pet's care and learning as much as you can even before you get your exotic pet is one of the best things you can do. Also, people who are successful keeping exotic pets are often happy to help out a newcomer to their hobby.
Observation: The most powerful tool next to knowledge of your species is the ability to be observant. A scale can make you aware of weight loss much earlier than by sight or feel. Disturbances in sleep cycle can be due to a medical problem. Lack of shiny feathers or healthy scales can tip you off that there is as problem, as can stools that are different in color or consistency. Any observation that you can make that is different that your pet's norm can be a sign of disease, and in exotics, the earlier we catch a problem, the more likely it is that we will be able to diagnose and treat it in a timely fashion.