Some of my input thus far:
1) Collect and explore. Seriously, spam that V button wherever you go, I've found so many chests and loot bags containing hundreds of gold + rare / unique items that were difficult to find (out of the way).
2) Some people try to hoard crating materials, realize that some crafting mats become "obsolete" as you level up (i.e you want tier 3 mats and have little to no use for tier 1 mats), go and sell these mats or turn them in for power.
3) Be on top of the War Table frequently. Always have some operations going on, you'll get gear (as crappy as common and as amazing as unique), gold, crafting materials, etc.
4) Save. You don't NEED that 10k gold unique 2h axe from the vendor, if what you have is sufficient then so be it. There have been times where I've purchased an expensive 6k+ gold item only to find an even better item in a dungeon a half hour later.
5) Allocate your inquisition perks towards gold earning things (merchants buying and selling for better prices, etc.).