If it's the hinterlands dragon, this one can be destroyed with use of the geography. Also on highest difficulty and was getting smashed, so anytime he lifted off I put my group underneath the edge of the mountain in whichever direction he flew in. IE, if he flew north, he'll probably come flying back with breath in a southeast/west pattern, and being up against the mountain let the over hang shield me. When it gets low health, it sits on the high point, near the landmark. Kept my party underneath the same mountain, firing ranged at it, and when he summoned dragonlings, they converged on my group at that same point. (Exception being the ones that spawn on their own ledges.) I also kept my party relatively close to the dragon while it was on the ground, that way they don't do the "range" breath attack, just tail swipe, that suck ability and I think a cleave thing.
Approach it like an mmo raid boss fight - I've been trying to avoid reading much in the way of spoilers, but I try to assume that's what it is. The most dmging ability from dragons has been that "suck" ability where it pulls you in, so I try to position the dragon in such that I can use the environment to shield me. The dragon in Crestwood was like this, where there were pillars nearby, so you could sit on the opposite side of the pillar and get blocked from getting pulled in by it.
The AI sucks; when I was watching at E3 it seemed way better at actually reacting to situations appropriately but I assume it was an isolated build for the trailer. I can't get those idiots to do a damn thing. Some of the dragon fights I ran with two mages - one full spirit, the other all dmg but also having barrier and dispel. Really wish I could find a way to make their barriers stagger better - I even tried to take control most of the time to do it myself but it was just so difficult battling with them. They were always on cooldown with the same time remaining, and I don't think it had a shared cooldown.
The AI has only ever helped me a few times - mostly for following. Had an issue getting some stupid crystal on a dumbass ledge, and I had put my party on hold, but one of them didn't take the command, so it followed me. Because it was trying to land right on my ass, it warped up onto the ledge I was attempting to climb onto. Switched my POV and done and done.
And fuck you Mix for that Morrigan spoiler. =/