-Download a Threat Meter. Watch It.
Yes, even you healers. It will warn you when your mage is about to tank again. DPS, it will keep your tanks from killing you (if you use it correctly, anyway). Tanks, it will let you know when you need mysteriously lose your taunt button.
-Download a Boss Mod. Pay Attention To It.
You can’t rely on someone to call out everything on vent, and vent lags. Failing that, learn to PAY ATTENTION in general. Holy shit! Someone is pinging their map on Maexxna? I wonder why? Oh look someone died. I wonder how that happened?
-Repair Before The Raid
“Hold on guys, my helm is broken,” is not something I want to hear three bosses into a raid.
Gem Your Gear
-Seriously, people. I mean even I get kind of lazy about enchants (there’s just nothing great for chest most of the time), but gem your shit. A little bit of research never killed anyone. Google: it is your friend.
Don’t Stand In Shit That Hurts
-Because your healers will rez you, then kill you again otherwise.
Enchant Your Gear
-Because everyone knows the quickest way to get an upgrade is to finally get around to enchanting something (true story: I finally enchant my chest, and…get…a replacement that night).
Know Where Your Debuffs Are Shown
-…seriously, people. “I didn’t know my polarity changed!” Also kind of related to the Boss Mod edict. If you’re too distracted to pay full attention to debuffs, they’ll usually yell at you.
Healers: Heal People
-If they’ve gotten a Frost Blast on KB, they need heals.
Addendum: Heal the Correct People
-If there’s AOE damage, don’t all focus on the tank, now.
Use Your Shit
-…you have buttons. Probably more than one or two. Learn how to make the most of them. Again, research never killed anybody outside of a few college students. And that may have actually been drinking related.
-Google is your friend. Preferably look up stuff before you get to the boss. If you fail to do that, don’t read 4chan while the RL is explaining.
Buffs: Love them
-Your Master o’ Fish Feasts might not be there. So have some tasty treats of your own. For progression content, I’d better see some damn pot buffs. Also, pots are useful for those of you who can’t heal yourselves or…use mana. Naturally holy pallys don’t use their mana bar, ever, so we’re exempt.
If You Can Get Rid of a Debuff, Do It
-Can you decurse? Cleanse posion, magic, or disease? Then do it. Yes, you, mister DPS. Yes, you, miss healer. I don’t CARE if someone else can do it too, or faster, or better, or what have you. Just do it. ‘Cause you know what? That other person probably is waiting for YOU to do it, and that sort of shit leads to wipes.
…I may or may not have seen every single one of these occur. Some of them even recently. And not in pugs.