Probably the most important tenets of AOE BRD:
• Put Straight Shot up first. I know you get used to doing Straight Shot AFTER your DoTs once you learn Iron Jaws, but that doesn't really jive with AOE pulls (unless there's one big beefy target in there, then feel free to do an Iron Jaws opener).
• Unless your tank sucks, you should be able to start applying DoTs as soon as the tank has done some action to the pack, even if they're still running to pull more.
• Mage's Ballad > Army's Paeon > Wanderer's Minuet*
• Don't forget to use Raging Strikes (preferably during peak RoD + Quick Nock spam). Foe Requiem too, if you can squeeze it in there; I usually forget.
• Invigorate and Tactician are your best friends.
Here's what I do, personally (in Lv70 duties, anyway):
Mage's Ballad: I usually put Windbite on everything (as much during the pull as I can). Once the tank stops moving, I hit Mage's Ballad. Spam Quick Nock once all the Windbites are applied. If there's one or two strong targets, then I'll apply both DoTs there, and make sure those don't fall off. If there's LOTS of targets, I generally stop adding more dots around ~6 Windbites; Mage's Ballad doesn't benefit from multiple procs at once. If the pull isn't mostly dead by the time Mage's Ballad is about to expire, I might try to Iron Jaws a few targets to prep for the next song.
*Bonus aside:
If Mage's Ballad falls off, but the pack is still-alive-but-almost-dead, and I know the next pull is AOE as well, then I'll pop Wanderer's Minuet at this point. It makes sure I still have a song up, but doesn't waste Army's Paeon, since I'll want that fresh for the next pull.
If that song isn't available...
Army's Paeon: I maybe spread 4 Windbites around. It'll hit 4-stacks soon enough. If this is the same pull as the Mage's Ballad one, then I may just need to Iron Jaws a couple targets. Quick Nock, Quick Nock, Quick Nock.
Oh, I see we're pulling back-to-back-to-back AOE pulls, huh...
Wanderer's Minuet: High TP: Spread several WindBites around. Low TP: I just apply the 2 DoTs to the strongest target. TP is probably really low at this point. Cut song short when Mage's Ballad is back up. If TP is dangerously low, focus on applying DoTs to conserve TP (and to prep for Mage's Ballad).
Once you've done enough AOE pulls, you just kind-of get a feel for what seems right based on how strong the targets are, how many there are, how many bulky targets are present, how much TP (and TP restoring cooldowns) you have, which songs are currently available, whether your tank is competent, etc. Different BRDs will apply different amounts of DoTs. You do you.
ShadowBringers is coming soon, and with it the removal of TP. This advice is sure to change soon, depending on how they handle that.
Does anyone know what happens if you pair Barrage with Quick Nock? Does it hit everything multiple times? Just the main target?