Throwing my half cent in here. It is has become abundantly clear that there are an influx of tanks recently. Unfortunately, as many of my comrades here have said, most do not take the time to learn and feel if they have a sword and board and throw talents in protection, they can tank anything.
Most of anything I could say has been said, ie, levelers who at 70 think they can automatically do heroics with improper gear, talent abuse, general lack of knowledge, a majority of players who are under the age of adulthood and in alot of cases could be even prepubescent thus not having a mature approach to group play. They see a raid, ooooh I wanna, they see arena, ooooh I wanna, they see Heroic something oooooh I wanna, and they hear that tanks and healers are always in need so they "attempt" to roll one. With 9, I think it has grown to 10M subscribers, you will get that quite a bit. Everyone wants the BEST of everything, the BEST gear, the BEST spec, the BEST class, and so on and think if they do it, then it will magically happen.
Hell Ive even run across those "experienced" players with great gear that still had no clue, and most respond as, well I got this gear didnt I so I cant be half bad, no, they just do it half assed.
My tank is primarily another tanking class, while I am leveling my warrior, the issues I have come across are truly unbelievable sometimes. Impatience, whether young or old, is inexcusable. Everyone wants to to rush and gets pissed when they die...
Some tanks truly want to learn and were focused on leveling that they rarely stepped foot in instances and require the appropriate learning curve, helping on lower level outlands dungeons are a good way to go, as well as those experienced, such as yourself, giving them THAT opportunity to grow. As long as they are up front with you and they need some experience, then help them. The more we do that, the more we will have tanks that are not as inept, particularly those that will never read wowwiki, alla, wowhead, or any of those other sites...so the only "guide" would be you or others who are willing to share their experience. Helping them get geared up to do the job.
The more and more we help one another out in the game, the better of you will be in the end, and I mean you in a general sense, not necessarily the OP. Even if you dont have the time to help gear them up, tell them where to go, or offer some advise on talents, or direct them to these boards.
Many warriors can offtank most things very well even in another tree, have them do that and work with a MT to learn a bit more, the warrior OT will provide a good deal of DPS as well. Also strap a hunter to your hip, they do have that talent/spell I think that focuses all aggro on the tank or whoever is marked, Mark of Death I think? Ive seen it but not sure if it is a talent, spell or other, but it is there.
The best guide are those people who are willing to help, as the good tanks in the game are the ones that usually were helped at one point or another, if they are not willing to learn or accept it, fine, tell em to f off and die, LOL JK, but ignore works well too :)