Do not water them too often, do not give them too much water & do not let them sit in water.
This is over watering, the number 1 killer of orchids. Giving them too much water or watering them too frequently or letting them sit in water keeps the potting material soggy, literally drowning the roots which then rot and die and, soon after, your orchids will die.
Phalaenopsis are particularly susceptible to over watering.
Do not let water stagnate in between leaves, especially new leaves & new growth.
Do not subject your orchid plants to direct sunlight.
Do not subject them to drafts from forced air heating or air conditioning or place them near heat sources.
Do not expose them to extreme temperatures or to too low humidity.
Your orchids will do reasonably well in 40% to 60% humidity (50% to 70% humidity is ideal). If your air is too dry (below 40%) mist lightly once or twice a day the unopened buds, the leaves and the top of the potting material. This will help keep your buds from drying.