The setup I'll outline below isn't perfect, but it works for me. I'm sure there are opportunities I'm overlooking, but the goal here is to put in a little bit of effort for a lot in return. If you've got ideas or tweaks I could employ to make this method more efficient, please leave a comment below!
Standard Setup - 4 CharactersLevel 3 Garrison with an emphasis recruiting followers with Treasure Hunter (increased gold rewards) and Scavenger (increased garrison resources). I have at least six followers with Treasure Hunter on each character, and nearly that many with Scavenger.
Level 3 Shipyard with a good cross-section of ships to counter threats.
Level 3 Salvage Yard for Big Crates of Salvage off of garrison missions. Logging in every day should provide you with roughly two-dozen crates per character per week.
Level 3 Profession Building to acquire profession materials used to make goods to sell on the auction house.
Trading Post to exchange garrison resources for profession materials.
Garrison Mission PrioritiesBased on the setup I'm using, there are certain missions I give priority to when gold missions aren't available---something that will happen if you're regularly completing gold missions across multiple characters.
Exceptional Items - like Medallion of the Legion, Frozen Arms of a Hero, Elixir of the Rapid Mind, the gronnling mount, and the fire corgi; these are all things that can be sold to other players for a hefty chunk of gold. I actually make several of these priority when they pop, like the Medallion, mount and elixir, since each holds the potential to fetch several thousand gold on the auction house.
Garrison Resources - nice to have an abundance of these at all times, whether for building/augmenting ships or purchasing profession resources from the trading post. Having a good chunk of followers with Scavenger should ensure you always have a surplus of resources for when you need them.
Apexis Crystals/Oil - I have these at the same tier because really, your need for these may vary. Having an oil rig on your shipyard will negate the need to collect oil from garrison missions. I will generally go for Apexis Crystals as my third priority because I use them to buy the 3 bonus roll seals each week for use in Hellfire Citadel. Of course, these seals can also be purchased with Honor and garrison resources, but for the love of Azeroth do not buy them with gold!
Level 100 Missions - once you've exhausted the above, remaining Level 100 missions that grant XP (or follower upgrades) are priority since they have the greatest chance of rewarding a Big Crate of Salvage.
Follower Upgrades - If you've been running your garrison for a while, most if not all of your followers should be maxed at ilvl 675. Still, these items can be liquidated for gold. Since making gold is the whole point of this exercise, and you'll also be getting a number of follower items from your salvage crates, they deserve their place here as a source of gold.
Everything Else - clearing out a mission makes room for another, so even if it means sending an ilvl 675 follower on a level 91 mission, do it. Keep all of your followers busy to maintain a steady flow of new missions.
Gold-Increasing Missions - these are different than the treasure missions rewarding gold and are indicated by the little star icon on your map: they offer a specific bonus to missions completed in that area within a certain time frame. One of these bonuses increases gold rewards by 100%. Knock these out first and pray a gold treasure missions pops up in that area.
Shipyard Mission Priorities
Other Treasure Missions - Complete these to make room for new treasure missions to spawn---hopefully ones rewarding gold.
Salvage YardIf you're knocking out missions daily, you'll acquire roughly two-dozen salvage crates per week on each character, more or less depending on the kindness of RNG. There are lots of valuable goodies in them, including old/current gear, profession mats, and follower upgrades. Each of these can be sold, or at least used to make more gold. I generally vendor all old-worlds gear that doesn't have a transmog value (hint: use TradeSkillMaster to easily determine this) and disenchant any Warlords gear. Given the price of enchanting materials on my server and the abundance of garrison resources, it's probably wiser for me at this point to start vendoring all gear. Profession mats get used to make stuff and follower upgrades get vendored. Depending on your take, it's possible to acquire several thousand gold or more per week per character via the Salvage Yard alone.
How you can utilize your characters' professions to make gold partly hinges on the health of your server's economy. Being on a server with a larger population has allowed me to continue selling Stage 1 profession items on weekly basis up to the present day. Additionally, bags, enchants, potions and flasks have been consistent sellers on my server. There may be a time, as I'm sure there are current examples, where it's more profitable to sell raw mats instead of crafted goods. That's up to you to determine based on your server. Personally, I pull in about 5-10k per week off of profession items I crafted using mats I purchased with garrison resources.
The key is, you should be getting all of your profession items for free via spending garrison resources at the Trading Post. Of course, wait until the post is visited by the garrison trader who offers your desired item at the lowest cost, which is 4 garrison resources per item.
There's probably some argument for continuing to utilize max level mines and gardens, but based on the rate I acquire garrison resources which I use to buy flowers and stone, I've decided it simply isn't worth my time.
BankerThis is a bit of a goldmaking 101 tip, but I always recommend having a character posted in an auction house who will act as your banker. Not only does this guy hold all of my gold, but he also gets mailed and posts every sellable item to the auction house. Mainly, this has been crafted items and transmoggables. Though having a designated bank character doesn't make you gold directly, as you could post to the auction house with any character, it does save you time. And you know what the goblins say!
I'm going to close this with the no-shit tip: try not to actually spend any gold as you're going through this exercise. Granted, spend your own gold how you see fit, but if you'd rather see your bottom line climb as quickly possible, you're going to want to practice pinching copper. At this stage in the expansion, there isn't a whole lot for your character to spend on anyway.
In utilizing this method, I've been able to pay for my WoW subscription each month while netting upwards of 100,000g in profit---without leaving the garrison.
What are you doing the make gold during the downtime between expansions?