- Is the Boss Dead (This covers a lot of sins - especially the first time)
- Did anyone/everyone die? (If so, why? Are they failing to grasp mechanics? Did someone miss an interrupt?)
- Are we taking too much damage? Why? (Especially if this is preventing 1, and causing a lot of 2)
- Are there adds? Are we handling them appropriately? (failures here readily pile up to impede 1 and build up 2, and 3)
If you really want to be good at this game, learning the mechanics, what you can do to mitigate or avoid them, and paying attention to your surroundings and events is just as important as knowing your rotation. You don't want to be the guy in the room who's tunnelling the bottom of their screen watching cooldowns such that they become a mana sponge for avoidable damage or, worse, that asshole who throws hissy fits at the healers because they're dying when they really should have dodged something they could see coming a mile away.
Pro Tip 1: Learn. To. Fucking. Interrupt. Regardless of Spec or Role.
There are many fights where this is vital so, for example, sitting there and going: "I'm a Resto Shaman, I don't need Wind Shear on my bar!", when you're doing Nefarian and one relatively cheap Wind Shear prevents 30/40K worth of raid wide damage you're going to have to use expensive heals to top off and is off the Global Cooldown table so you can go immediately back to heals is pretty fricken dumb. In this case, damage prevented is mana saved. If you're DPS, it's not "Bitch Duty" when the boss won't die if you don't do it: it's the most important job on the floor. Likewise, tanks that don't interrupt, despite still achieving massive threat leads, and then scream that their healer let them die because said healer just got feared, for example, make me cry. If you think we won't know you're not doing this, you might want to wander through some of the other statistics Recount/Skada tracks next time you're on... (and that's before we feed the logs into WOL and the likes for analysis)
You can turn on nameplates and enable spell cast bars in the Interface menu to make your life easier for those non-50' tall critters but you may want to look into mods to get your enemy castbars more readily in view.
Pro Tip 2: Know your glyphs and keep a stack of Dust handy.
While more true for the later, your Primes and Majors tend to have one or two really situational glyphs in them. Knowing what those are, and which fights you want to abuse them on, can improve your DPS output or survivability for the exertion of all about 15 seconds of adjustment and a few gold.
Pro Tip 3: What do I bring to the fight?
Can I root adds? CC? Interrupt like a bastard? Soak tons of damage - even as DPS - through cooldowns? Know your toolbox so that when you're standing there for the first time and something happens you know, instinctively, how to respond to it or can suggest how to attack the problem if you wipe. Sometimes, you want to just try some of those things the first time to see if they work or not because it's more important to know what you can do in the future if it's not likely you're going to kill the boss.
Pro Tip 4: Keep your head up coming across the blue line or...
You can't play this game with your eyes on the bottom of the screen chasing action bar buttons while shit is falling around your toon mid screen. You're going to miss visual cues, that patch of fire under your feet, the buff that just went up in the boss window, or the curse that just landed on your buff bar. Tunnelling like that's going to frequently make you either a mana sponge or dead, depending on the whims and tolerance of your healer(s). Worse, it's going to make you a liability in the eyes of any raid leader who you're not sleeping with or is your drinking buddy and cause you to get bumped in short order.
So, what do you do? Start by learning the Keybind interface and getting your abilities mapped in a manor that's comfortable and intuitive to you. It doesn't matter how others do this if you can't execute with it. Thus, experiment and get something tailored to your own ability/playstyle so you can execute without looking. Next, figure out what you need to track to play your class/spec and then research and look for mods/addons that help you do it. There are often "packs" or individual items on offer that will help you track it all for your class and, most importantly, let you place the tracking elements on the screen such that you can better keep your eyes on what's going on around your toon and avoid the damage that you were having problems with before.
Just remember: packing so much stuff centre screen that you can't see what's going on around your toon isn't going to help either. Figure out what matters, get it centre, and use the rest of the screen to help you get used to scanning around. The goal here isn't just to get you tunnelling a cup sized circle centre screen instead of your action bar, it's to make you more aware of what's going on in the fight by letting you take your eyes off the bottom of the screen. If your job is to root the adds coming in from the left and now you're so focused centre screen that you don't notice them until someone starts yelling at you then you're still not doing what needs to be done as well as you could be.
Get comfortable with letting your eyes wander. As long as it's not onto your Girlfriend's Friend's Boobs. We don't need that drama in vent...