How To Quickly Kill Your Orchids

Let water stagnate in between leaves or new growth.
This will cause rot that kills plants like Phalaenopsis and kill the new growth of other orchids.

Water them too often
Orchids can not stand a soggy potting material as this destroys their roots and promotes rot of the plant.

Let them sit in water
Water will accumulate in a cachepot without drainage or in a decorative basket with a liner to catch the water. Roots of orchids need a lot of air. If they are flooded with water they will die and this will be the end of your plant.

Subject them to direct sunlight
When subjected to direct sunlight, buds will dry and fall, flowers will fade, leaves will burn.

Subject them to drafts from
air conditioning or forced air heating.
The air from these is usually very dry. If it blows even faintly on your plants it will dessicate them in just a few days.