Welcome to the site! It's good to hear that you're enjoying tanking, because it is much more fun than it's made out to be.
Mobs in heroics hit much harder than anything you'd expect to see when you're soloing, PVPing or in certain normal instances. Your gear is not at fault here; the healer has to be on the ball too. If you really wanted to, you could wear more avoidance if you feel like you're taking too much damage but in my opinion avoidance hurts your threat generation too much in heroics, which leads me to:Damage Taken - One small problem so far is that I do get hit pretty hard some times when I'm tanking heroics. It's generally when I have a resto druid in the group and he doesn't put HOT's on me. If I have HOT's I seem to be fine for some reason. I always try to keep shield block up for the entire time I'm tanking.
This isn't always your fault. If your DPS are too trigger happy, they'll pull off you no matter what. Get them to hold off on their big nukes for a couple of seconds while you build threat. That said, there are things you can do to improve your threat yourself. You can stack expertise (which is an amazing stat by the way) and hit, as well as shield block value and use a higher DPS weapon to improve your Devastate damage. As I said before, too much avoidance can cause rage starvation if you get an (un?)lucky avoidance streak.Threat - I seem to have no trouble holding threat from anyone bar mages and warlocks. It's interesting to note that some warlocks or mages will steal agro but when I have a look at their damage on the damage meter it's lower than the other dps in the group. I've been in some groups where the damage thrown around is massive and I have no trouble holding agro. I use the rotation 2 devastates, revenge, shield slam and then put shield block up. On the initial pull I also try to taunt the mob so I get a chance to build up some threat.
Multi-mob tanking is our class' weakness. What I do for the 8 mob crack elf pulls is mark as many as I can for CC then hit a Shield Slam on one (when I spec Prot obviously), a couple of Devastates on the rest then tab between them using a couple of attacks on each with more time spent on the focus target. This is somewhat of an acquired skill. As for the mana wryms, I don't even bother. I TC and Demo Shout and Intervene the AOEer, saving Challenging Shout for when someone is about to die.Multi Mob Tanking/AOE Tanking - I REALLY struggle here with AOE tanking. Especially in Magister's Terrace with the mana wraiths and 8 mob undead pull. I just can’t hold agro with Thunder Clap and Demo Shout.
Heal Agro – Often I find myself in the position where I have 4 mobs coming to me and I need to multi tank at least 2 of them. I’ll get 2 Devastates off on the first mob and then by the time I’m trying to grab the 2nd Mob it’s already agro’d onto the healer. How can I stop this?
As for healing aggro, you can either ask the healer to wait until you hit all of the mobs at least once before healing, or if they really need to heal you you can Intervene them and pick up any mobs on them. Thunder Clap is also good for initial aggro here.
Aside from the obvious pieces that need gems/enchants, your gear is quite solid. You can afford to drop some defence because you have 35 resilience as well. I'd suggest replacing [item]Dabiri's Enigma[/item] with something else like [item]Commendation of Kael'thas[/item], [item]Moroes' Lucky Pocket Watch[/item] or whatever else drops first. Keep running Kara and heroics for badges and check out other threads here about what badge gear to get first.Also could you have a look at my gear and suggest any refinements I should be looking at making there. Should I be looking at going to Gruul’s to get my shoulders and so on…
Hope that helps a bit