Cut leaves any time after they begin to turn yellow since no amount of care can restore them to their former glory. Use sharp clippers that you sterilize by wiping the blades with isopropyl alcohol, which helps to prevent diseases.
Cut yellow or brown leaves completely off the plant by snipping carefully at the base, where each leaf grows from the plant. Be careful to avoid cutting into the orchid's main stem.
Cut spent flower stalks back to their connection point with the plant. For phalaenopsis, or "moth" orchids, cut flower spikes back about half way, leaving two or more nodes, from which another flush of blooms will often grow.
Cut off dead and dying leaves on a regular basis throughout the year to keep your orchid tidy and healthy.