First take away leaves from coriander bunch and wash thoroughly.
Now keep on strainer to drain all water.
When it becomes little dry, then spread a clean cloth in shade and spread leaves on it to dry completely.
After each day leaves will shrink and become dry
When leaves start releasing crisp sound while holding, it means they are ready to preserve. Otherwise dry for some more time.
Now store in airtight container in refrigerator and after each usage , preserve in same way.
My tip: In winters fresh coriander leaves are available In abundance. So its better to preserve it for summers. Always dry in shade to retain green colour of leaves.