One thing I'd love to get better at when tanking is knowing what all is going on around me. Usually when I'm tanking I know where I am, where my mob is, and which way he's facing. If I'm doing well I might know where some of the other folks are standing or where I am in the room. And I'm pretty good at avoiding fire / green shit / void zones. But I seldom have a clear picture of where my ranged DPS is standing or where the squishy healers are so that I can intercept adds.
Part of the problem is the dreaded Bear Butt Syndrome. When you're tanking the camera seems to end up behind you and all you see is yourself. It's pretty easy to address this. Fiddle with your UI options so you get full camera control and max zoom out distance. (Even better, increase your camera distance further with a console command). Swing the camera around so you can see the rest of the fight. If the room is tall I find having the camera directly overhead often works well. Or 180潞 around so it's facing you.
The other problem is attention management. I'm often so worried about my DPS rotation and watching my health that I'm not looking at what's happening around me. But that's a silly place to spend my attention; I should be trusting the healers with my health and my DPS rotation is as simple as pressing 1 24 24 24 1 24 24 24. I think it's interesting that the best raid leaders I've played with have all been hunters or used to play hunters. I think the challenge of managing a pet, laying traps, and keeping range teach hunters how to pay attention to what's going on around them. Good skills to build.
One help for knowing when something needs your attention is an addon that shows you who has aggro. ag_unitframes nicely colors people's bars red if a mob has targeted them, a good indicator that something needs tanking. Main tank targets can also be useful, particularly if targettarget is turned on so you see who the mob is targeting.
Awareness is less of a problem if you know a fight well. I wiped us on Leotheras last night because I didn't correctly position him in the split phase and he went whirlwinding around killing DPS. It's only the second time I've seen him and I wasn't totally clear on my position vis-a-vis the warlock tank. Also, I didn't know exactly where I was standing and how to get to the middle of the room. I certainly won't make that mistake again. But I'd like to develop the skills to see problems like that as they happen before I learn the fight.
Any other advice for how to know what's going on around you as you tank?