The foremost reason for orchids killed by a newbie is by overwatering. A newly potted orchid has most of its roots damaged and cannot take up much water. Watering too often will kill it. Humidity around the plant needs to be increased while watering should be kept to a minimum. With established plants, there are several factors. Plants in clay pots, an increase in temperature or plants in a breezy environment need to be watered more often while watering needs to be decreased during the monsoons, in winter where it gets really cold as well as for plants grown in plastic pots.