Rare plants are usually rare for a reason--either they have a limited habitat or are difficult to grow and propagate in cultivation. It is possible to properly grow exotic rare plants, but the key is to understand what the climactic conditions are of their native habitat and to ask others who already grow them successfully. Then provide the ideal conditions for each plant as exactly as possible.
Many plants are adaptable to variable lighting conditions, but specialty plants and rare exotics often have special needs and are not very adaptable. Consider where the plant naturally grows and what kind of daylight it gets in its habitat. Many tropical exotics are accustomed to full tropical sun, while others rely on the dense jungle canopy for protection and prefer deep shade. Full-sun lovers may not grow or have poor growth without enough light, and shade plants will burn in the sun.
The average temperatures of the native range of a rare plant need to be considered. Some areas like the desert get very warm during the day and cold at night. Some plants require a dramatic day to night temperature variance in order to grow properly or bloom. That may not be possible without specialized equipment like a greenhouse that replicates that habitat. Some plants come from areas that never receive frost or a freeze, while others require a dormant period and a heavy freeze to set flowers for the next year.
Rare plants from tropical or boggy areas often require a constant high humidity level. Most plants prefer a stable humidity regardless of their requirements, but some delicate types will dry out quickly and die if it gets too low. An unstable humidity level can lead to pest infestations such as spidermites in many plants.
The general rule for most plants is to water thoroughly then let the plant dry out slightly before the next watering. For rare, delicate plants, learn what the average rainfall amounts are in its native habitat. Many plants come from areas where there are only two seasons, wet and dry. Some may need to completely dry out or have water reduced for a few months of the year. The amount of water a plant needs also differs depending on the type of potting media used.
Small-particle soil retains more water than soil with large particles. Plants from boggy conditions may wither if they dry out but need a stable soil that will not rot easily. Some tropicals are epiphytes, meaning they grow on other living plants and do not have any soil around the roots at all. Lithophytes grow directly on rocks with their roots anchoring between cracks. Terrestrial plants grow in the soil.