Aethril is a herb found in Broken Shores, and is currently worth a lot on the Auction House. In this guide you will learn how to farm it efficiently, getting about 5 stacks per hour (and each stack is 200 Aethrils). You should be a level 3 herbalist in order to get the maximum amount of profit, but if you are lower you will get to level 3 pretty fast with this method as well.
For this method we only farm two nodes in Azsuna, and constantly use an add-on to serverhop and look for spawns. The add-on for this is called Cross Realm Assist, but there are also other alternatives available.
To start, go to 54.88, 54.73 in Azsuna and loot the node there. Now walk the 5 second walk to 58.88, 53.11 and loot the node there. These are your only two spawns, so now use a serverhop to change to another realm. There are usually at least one node on each server, so pick it up, and then change realm again! You should be able to pick almost 1 000 herbs in one hour with this method, so you are looking at getting 15-20k gold per hour, depending on the price on your server. You can get even more gold by using the ingredients to craft stuff with inscription and sell it on the Auction House.
The method is, as you can see, really easy, but also very boring. However, you get a good amount of Aethril very quickly, so it's nice to do while you watch Netflix or something on the other monitor. There are no mobs close by, so there's really nothing to worry about while you are farming.