Threat is a joke -- don't flask, eat, pot, gear, gem, enchant or reforge to get more.
Well, that would make this a very short blog post. Especially as the above statement basically is all that you need to know.
That's also the short short version.
The short version is that if you don't know what to do, then you should follow the above statement.
Then there is a long version as well, and this is where my blog post stops being very short.
Threat is a joke unless you have zero vengenance and zero threat lead. That's usually just before you start pulling, but it sometimes includes tank swap situations, new adds that have to be picked up and fights with threat reset mechanics. While you should have some vengenace up at the moment when these exceptions occur, your vengenace could very well be low enough that threat initially isn't a joke.
If you can rely on hunters and rogues diverting threat your way, then you're potentially not being very casual about your tanking. Sure, member of a casual raiding guild where players still do their job, but those groups tend to be the exception.
Now, if you can't rely on anyone helping you during those moments when threat is not a joke, how should you handle my first statement in this post? Exactly the same way as if you could rely on help.
The thing is, if you're geared for threat in a fight that could kill you even if healers do their jobs decently enough, then you're gearing wrong. Does that mean you just have to bite the bullet and watch stuff run all over the place and then complain about careless dps? Well, both yes and no. Yes, you have to bite the bullet. No, stuff isn't allowed to run all over the place. It depends wether you should complain about careless dps.
Just bite it.
A dead tank generates zero threat. You absolutely have to cover the gearing needs to stay alive. That's simply not optional.
Don't allow stuff to run away.
You have two taunts on an eight second CD each, and they're off the GCD, and they can't miss. If you lose threat, just taunt. Effectively you just got a 10% threat lead against melee dps and a 30% leads against anything else (provided healers are standing away from melee range).
If you're raiding then pots are worth it. Break my initial rule and drink one for a big strength increase just prior to pulling.
Use Divine Plea and Inquisition pre-pull for some extra threat. Use glyphed SoT seal for the pull. When things are under controll you can swap to SoI for increased survivability.
If you know well before the fight that adds are going to pop up with the intent to eat your healers (and the occasional dps) for dinner, glyph dazing shield. While it delays the time it takes the adds to reach you, it also delays their dinner preparations.
Taunt. The two taunts are still there long after your initial pull. Be careful with the RD though. You might taunt something you didn't want to.
If you're tanking one caster add and you realize you have to walk over and disrupt that dinner making mob, there are a few options. AS available? Taunt the far away mob, AS the one you're tanking and start walking. No AS? Stun your current target and walk away. Either you'll have to get back to the caster, or your AS came off cooldown and you can order it to come over to you.
You're truly stuck in place with your current target. There is simply no way you can walk away from it for one reason or another. And a caster chef just popped up a bit away. And AS is on cooldown. Taunt the new mob. Divine Plea, Inquisition, taunt it again and Judge it. AS still off cooldown? Stun your current target and cast Exorsism on the far away mob. AS still on cooldown? Your first taunt just came off cooldown, use it again. AS still on cooldown and that mob starts working on your healer? Well, HoP your healer.
And then there are the oddball situations when you're seemingly out of options. You're getting swarmed and nothing could possibly make you collect all those adds. Well, there are oddball solutions. They're likely to fail, but if the alternative is a guaranteed fail, well. You have two instant heals. Lay on Hands is a nice threat spike, and while Holy Radiance only ticks for about 1k health per second, if you're standing among melee dps it stacks up pretty decently. You're having RF turned on, but your healers aren't. Instant healing might be enough to make anything in the area lose interest in them.
And finally there are the situations where you're simply doing it wrong. You have AoE attacks for a reason. What works on a single boss doesn't always work on a group of targets. You also have a tab key. Noone's going to yell at you for changing target, get in a good smack and continue to the next, all while keeping your AoE attacks up. Just make sure to get back to your primary one rather quickly.
To complain or not complain, that is the question.
If you haven't tried beefing up your initial threat, then you have no right to complain. Now, if you truly believe you've done your part (and haven't been proved wrong) then some complaints might be in order.
If the dps are hysterically outthreating you during pull and they still want you to tank the content, then they should take it easy at the start.
If the dps are still outthreating you after thirty seconds of the fight has passed, then either you can't tank for them, or they'll need to accept to perform under their level. This would most likely be a bad case of tanking, ie you need to learn how to tank, or they're outgearing you badly. The latter might be the situation when you're replacing a previous tank in a guild but simply lack the gear to do the job as well as they're used to.
If you're outthreating every dps minus one, who isn't doing noticeably higher damage than the rest, then that tank wannabe should be told to turn off threat increasing abilities.
But what about threat gear? Well, the exceptions to my first statement is not a topic for this post, but I'll cover that later.