Shred curry leaves by hand just before you drop them into the cooking pan. This releases the aroma from the leaves just in time for it to be absorbed into the food. Dropping whole leaves is not as effective.
Modern living means that not everyone has the luxury of obtaining fresh leaves straight from a plant every time they cook. So whenever you obtain them in bulk, simply make sure that there is no apparent moisture on the leaves and then store them in an airtight container in the refrigerator as soon as possible. This ensures the preservation of their freshness and green colour.