It is best to leave the Pods deactivated on the mouthpiece or in the airtight Pod pack.
The beauty is that active consumption of the Pod only occurs when air is flowing through it. This, in turn, only happens when you have the Pod activated. By sliding the Pod on the mouthpiece, you can activate and deactivate the tasty airflow.
Unfortunately, a little aroma still evaporates over a longer period. But you can slow this down by putting the Pod back in the Pod pack while you're not using it.