In this day and age of gogogo speed heroics, DPS players sometimes have a hard time knowing when it's safe to open fire on a group of mobs - or rather, most don't seem to care at all, opening up with full bore AOE as soon as soon as they're in range.
You could argue that a "good" tank is already aware of this impatient mindset and knows to adjust their opening rotations accordingly. The reality, though, is that tanks come in all flavors and levels of experience, so blasting away is just more likely to cause needless chaos and repair bills.
Remember that when your tank has to taunt off you or reposition, they're wasting time which they could be using to build more threat. So once one mob gets loose, it becomes much easier for others to get loose, too.
In order to do your part as a DPS Pro, there are certain audio/visual cues that can help you do your thing without pulling off the tank:
Death & Decay is what you want to watch for, which is a reddish-colored ground-effect AOE accompanied by a woosh sound. However, with many specs, it has a long-ish cooldown and can't always be used every pull - so they'll also use Pestilence (dark/smokey lines that shoot between mobs), Howling Blast, and/or Blood Boil (both sound like mid-rangey explosions).
TLDR: wait for some combination of red ground, dark smoke between mobs, and/or explosion sounds.
Contrary to popular belief, our furry friends can make excellent AOE tanks, as they come equipped with a spammable Swipe ability (no target limit, 360 degree radius!). This has a red claw/scratch-like graphic and a cut/bleed sound. They also have an AOE threat roar, that sounds like... y'know... a roar. And has a cute standing-bear effect, which apparently terrifies mobs.
TLDR: wait for a few scratch sounds and until all mobs are in melee range of your bear.
Most folks are familiar with Consecration, the yellow glowing ground around your friendly neighborhood Tankadin, which nicely distributes AOE threat to mobs around him. However, it's not always the first ability to be used, as they also have two great multi-mob abilities that are often used first: Avenger's Shield and Hammer of the Righteous. The shield is a ranged ability that flies out of the Pally, leaving a bright trail behind it. The hammer can hit up to four (glyphed) nearby targets and has a signature brrrrang sound.
TLDR: wait for clangy sounds and yellow ground before going nuts.
Much like the druid, some incorrectly assume that warriors have a hard time establishing AOE threat, but I've seen some very talented wartanks handle large packs with style: you'll see them Charge into a pack, lay down a Thunder Clap, maneuver for position, then blow Shockwave, stunning all the mobs. When executed well, it's very impressive to see! The clap sounds like an electrical explosion, and causes cracks to form under the warrior. The shockwave sounds like a low-range boom, and has the visual smokey wave-like effect.
TLDR: wait for thunder and lightning sounds before pulling the trigger.
So there you have it - the handy guide to improving pull stability! So stop staring at Recount, learn the abilities of your tanks, and everyone goes home happy - as quickly and efficiently as possible. :)