Rewrap your chocolate tightly in its original wrapping, if possible. If unavailable, wrap tightly in a zipper bag (with air squeezed out), foil, cellophane or wax paper.

Then place in an airtight container. Remember, air is the enemy of freshness.

Store chocolate in a cool, dry area and away from a warm and/or humid environment.

Keep the chocolate out of direct sunlight and away from any strong artificial light for long periods. 

Store chocolate bars for up to a year wrapped tightly, away from insects, air, and sunlight.