I'm going to keep this very short and clear.
Go to the Sentinax zone and create a 5 man group.(1/1/3 preferred) [does not work with a raid group]
Get a spot near 1 or more portals.
Start stacking and farming mobs
What to do:
When green and blue items(beacons) drop, you can use them to create more portals or empower the portals around you.
What not to do:
If by chance an epic item with the name "Portal-Stone: xxxxx" drops, DO NOT USE IT! If the item is used, it calls a big boss that takes forever to get down and after the battle you need to wait 5-10 minutes for the portals to respawn again.
How much did I make in 1h?
A total of 12k nethershards
Credit goes to ITSSKITZ for this guide
If you want more details about this method check the video below: