I shouldn't have to say this, but there are SPOILERS in this list.
I'll just list my play order and you can decide whether it works for you. This includes ALL zones and likely WILL leave you out-leveled for a portion of the game. However, my primary goal is for story progression, not difficulty. To determine the story order I relied on NPC dialog as well as Codex entries available within the zones (such as those regarding the Freemen or Red Templar activity).
DISCLAIMER: I play on Casual, so you might need to be a higher level to do some of the missions than my recommendation if you play on a higher difficulty. I've also never completed a templar play, so I don't know if some of the content of the Hissing Wastes (or Emprise du Lion) changes based on that due to the concentration of Venatori activity.
NOTE: The term 'urgency' is used to describe the level of urgency given to certain events due to NPC dialog or other factors. Yes, you CAN leave the events for a later time, or never complete them at all, but that would require you to completely ignore NPC pleas for help and such, which I feel takes away from the immersion if you just expect the game to wait for you to take your sweet old time. (My comments regarding Hawke below do take this into consideration, in addition to the urgency created by talking to him/her in the first place. IMO it's a balance and you have to decide what feels right to you.)
If, like me, you are concerned about being too over-leveled for some of this content (but still want to complete everything), you can certainly avoid turning in most of the quests (particularly in the Hinterlands) until the end of the game. I typically complete everything, but leave finished quests sitting in the log until I'm ready to turn them in.
1 Hinterlands
----- In Hushed Whispers / Champions of the Just - I strongly recommend doing either of these as soon as possible. You can get the required Power Points by setting up camps, closing low-level rifts, recruiting companions, and doing some miscellaneous Haven quests, thereby leaving most of the Hinterlands untouched for later exploration with the full party of your choice (including Dorian + Cole), which is not available until after you arrive at Skyhold.
2 Storm Coast
----- In Your Heart Shall burn - Again, I do recommend doing this early so you can stay within the level range of some of the zones. After arriving at Skyhold I avoiding talking to Hawke at all because that simply sets the urgency ball rolling. I wait until I'm ready to head to Crestwood and begin the whole sequence of events leading to Adamant.
3 Fallow Mire
4 Exalted Plains (civil war, part 1) - Do NOTE that if you leave all of the civil war stuff until after the Winter Palace some of the dialog with NPCs is (can be) different.
5 Forbidden Oasis - This zone can really be done at any time, or never if you don't care for shard collecting. I place this here for personal RP reasons.
6 Crestwood - Due to urgency, I recommend taking Caer Bronach, draining the lake, and closing that rift before leaving the zone, even if you don't do anything else there.
7 Western Approach - I suggest taking Griffon Wing Keep before leaving the zone.
----- Here Lies the Abyss
8 Emerald Graves (civil war, part 2) - I recommend resolving the final Freemen of the Dales conflict there before moving on.
----- Wicked Eyes and Wicked Hearts
9 Emprise du Lion - Be sure to clear out the mine, take Suledin Keep, AND talk to Mistress Poulin again before leaving the zone. Because of Codex entries found in the mine, I recommend completing Red Water area after clearing it out.
10 Hissing Wastes - This can be done before or after What Pride Had Wrought. Because of the structure of some of the dialog I recommend after, leaving the final missions to be done in succession.
----- What Pride Had Wrought
----- The Final Piece
----- Doom Upon All the World
EPILOG - Enjoy the party + optional boy/girlfriend time
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11 Jaws of Hakkon DLC - Due to the level requirement, and it just making sense that you would undertake this search after the world is saved, I recommend this for post-game play.
END (until the next DLC is released).