Most plants that show yellow leaves mean that they are getting too much water. Overwatering is the main cause of death for container plants. Now some snake plants feature a yellow edge to the leaves so do not confuse this pretty highlight for damage. If the whole leaf has turned yellow, remove it. Once a leaf has gone yellow it will not return to health.
When you water your snake plant, check to see if the soil has dried. If the soil is moist, wait a few days. The plant should be grown in a type of soil that does not retain moisture. Use a succulent mix or add coarse sand to regular potting soil.
Occasionally, old leaves will fail. This is natural. The older leaves on the outside of the plant will eventually die.