I would recommend a nameplate addon. Any nameplate addon, really.
What’s important is that you have one which changes colour (or size) based on threat so you can tell at a glance if everything is hitting you, or if you’ve got a stray add hitting someone else.
Having a weakaura which keeps track of all your resources (especially defensive cooldowns) is never unwelcome either.
Bear is very straightforward and very strong right now. You build Rage with Thrash and Mangle, and you dump rage on Ironfur or Maul/Raze depending if you want to decrease damage taken, or increase damage done.
Realistically, the average Tank spec is significantly easier than the average DPS spec in complexity. The difference between the Tanks is more about what are the “extras” you want to provide.
You play a Blood DK if you don’t want to rely on your group for anything.
Warriors are what you want to play when you want to get from A to B to C and then finally D before the rest of your group even makes it to A.
Paladins have by far the best group utility.
Bears are kinda good at everything, but not as good at whatever the other tanks are specialized in.
Monks are…complicated. They DEFINITELY have their strengths, but it’s hard to utilize those strengths outside high-end tanking.
Not an addon, but it’s always the DPS’ fault. 
Jokes aside, you just gotta be able to shrug off what you can’t fix. If a DPS pulls extra and your tools to pick them up are on cooldown, not a whole lot about it you can really do.
It comes with experience, but eventually you learn the places where you have to account for mistakes and those you do not. A good example is the little skip you can do in Freehold after the first boss.
Never assume that everyone will make it through and always be ready to pick those mobs up since someone will facepull a good 60% of the time.
Blood DK’s are significantly less stressful when you’re tanking on them.
They’re all about resource management. If you space your cooldowns well and don’t run yourself out of runes or runic power, you’re basically immortal.
It’s a very fun, very unique playstyle among tanks. Probably my favourite, but it’s not for everyone.