When it comes to garrisons I like to make sure to max a Inn to level 3, this will unlock treasure hunter missions in your garrison and shipyard which can earn you anywhere from 40-2000 gold each from what Ive experienced. Also every week it allows you to recruit 1 new follower with a trait or ability of your choice. always pick treasure hunter becaseu this will double the gold you get from missions making your missions worth 80-4000 gold. (this ability is stack able if you put 2 followers with the treasure hunter trait on the same mission.)
Max your shipyard to get the most worth wile missions.
Lastly max your herb garden and your mine and sell the mats you earn in stacks of 200 on the AH. These building will be earning you the most gold from your garrison.
Here is a list of legacy raids to run for extra gold:
http://www.wowhead.com/guides/raiding/gu...up-classic
Every week I run all the cata raids and on
heroic 25man looting all items over one gold then selling them to vendors. They are easy to solo and will pull in about 6k gold. I also run ICC and uldum for my chance at invincible and mirmons head following the same method which earns about 800g each.
Let me know if this helped. Also if you're on Sargaras feel free to add me!