I killed my first dragon at level 12,
. I tried at level 10 and 11 but couldn't do shit and never got the beast down 25% in HP. I was with Cassandra, Varric and Solas at that time.
When I got Iron Bull I switch Cass for him and also switched Solas for Dorian (but I think i'll bring back Solas).
So I went to that dragon in the spoiler tag at level 12 (as a S&S Tank) with Iron Bull (2H DPS), Varric (Ranged DPS with some sthealth stuff) and Dorian (in full Fire mage DPS mode). This time it went like a charm. Not an easy fight but went very well. Took about 10 minutes to down the thing and it was really satisfying. But two characters died during the combat.
I also killed my second dragon yesterday in
, this onw was not easy either and everyone died except Iron Bull that landed the final blow, it was awesome!
I know I should get other potions and maybe the upgrade to 3 potions carried/more potions but I always equip the Health Potion and the Regeneration Potion on all characters. Can't go out without them I guess. The Regen potion is very useful when your charcaters are at 50% HP, you pause and pop one on each low health characters and resume the fight.
Thing is, I found out I freaking HATE the "before combat prep" in these games. Popping some DPA boosting potions, some spells and go in...dunno but I find it boring as hell. Reminds me of my favorite class in the NWN series, the Cleric...but to be good and effective I had to cast 5-6 spells on the groups before going in, everytime, and then rest. It was mind dumbing and boring...but I loved the class lol.
So I tend to just bring HP/Regen potions and pop them when I need to.