The efficiency of farming AD, changes a lot from module to module. During Storm King’s Thunder, you could make a ton of AD by farming Lanolin. When new modules are released, be sure to look out for all sorts of items and currencies that can be farmed for NeverWinter Astra Diamonds.
Dungeons can also be farmed, but up until you can do Fangbreaker Island and the dungeons of the later modules, you will mostly be limited to farming for salvage (see further up).
Tip: Be sure to use leftover campaign currencies to buy keys for various dungeons. In some cases like the later dungeons, farming campaign currencies to get more keys is vital. Also remember to claim your daily keys from VIP and get you daily free key from the Dungeon Chest Keymaster in PE.
Dungeons, Skirmishes and Trials
Fangbreaker Island, Spellplague Caverns, Tomb of the Nine Gods and Castle Ravenloft are only accesible to end-game players but when you get to this point you can farm these dungeons for valubles like masterwork resources and Ultimate Enchanting Stones.
Illusionist’s Gambit can be farmed for companion gear that can be sold or salvaged, some of it sells for millions of AD but is very rare.
Farming and selling Hunt Lures and Wanted posters can be profitable, but prices vary a lot, so check those first. Currently at mod 14, profitablility is low.
NeverWinter Farming campaign items and currencies can be a great source of income, but mostly at the start of new modules, when the prices are high. Currently at mod 14, profitablility is low.
Dread Ring daily lair quests: After completing the Dread Ring campaign and getting your Adamantine Gauntlet, go back to Dread Ring every day to get the daily lair quest from Sergeant Knox for a chance at a GMOP or SMOP, along with a good chunk of RP. Only 5 minutes of work.