Industry

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Industry can be Activated, Upgraded using Materials and Gems, and Deactivated. Deactivating an industry won't undo your upgrade, or the buildings built in town (allowing you to reset industry after finishing the buildings). 
You can get industry points from Associations and Ranking Up.
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-Get the 5 Industries for element dungeons to lvl 3. 
-Get the Town Industries as needed. 
-Get the Dungeon Closure Reward to max. 
-Don't get the Road Industries that decrease exploration time as MBT alone can cap areas and is easier to acquire early. 
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Consider getting the Industry for Station Stats (the 2nd one with most jobs) to max, to help meet stat requirements for Fortresses. For Explorers focus on MBT to reduce turns further, LUK and DISC are optional.
The Domain Capture, Fortress and Shrine industries are debatable grounds, and don't bother with any other on that page. For these three, the % is multiplicative, not flat. So, max fortress industry increases its rate by half a percent or so.
Finally, get Mythic Weapon Crafting to craft event gear.
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Consider getting the Road Industries if you've gotten into detailed exploration since you'll start capping out on Companion MBT Limits. 
Element Dungeon Lv 4 is for Immortal Dungeons, which are mainly for Immortal Materials as Legendary are easily acquired from Fortresses which require no extra investment. It is advised to only pick this up when you have a good income of Legendary Materials for Expansion and Mythic Stationers built (1.15k PRD/MNG) to Invest into Immortal Dungeons as you can always buy the Immortal Materials off AH instead by selling the Expansion materials. Later on you can also sell the immortal Mats if you can sustain it.
Element Dungeon Lv 5 should only be done very very late as it requires a hefty amount of materials and a Fantasy Companion (or nearly Maxed out Mythic+10) but gives the more expensive Immortal Mats
The dungeon farming industries can be very useful to empty out dungeons faster, but you can just use Gear Refines for that as well.
You can consider getting the Quarry industry, but it's not a requirement.