I have a 70 warrior too, and I need to get better with tanking. One of the reasons I'm here. When I get the chance, I'm going to practice the tab button thing, and see how it works. I think my main problem is the cc is too close to TC, making me try to move while holding multiple mobs, and the dps doesn't burn down the target I'm on, they go after whatever they want. Doesn't help that I still have some 5-man regular instance pieces.
Here's the point: in my opinion, Challenging shout should be used only as a last resort, like when you get a big pull, and the dps'ers/healers pull aggro from you. As for just any pull, or before you really need to, it's a long cooldown to use, when you may need it a little later. Another thing I would recommend, is to have the dps'ers hit the target you are working on. That way your Cleave, TC, etc. will hold them from the healers, while the dps isn't in danger of stealing your mobs. Along those lines, KTM or Omen threat meters are very good things to have.
Sorry so long, but I hope it helps.
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Goosetanker Nelf Warrior (Wildhammer)
Wersmyfrends Human Mage (Wildhammer)
Wersmyfrends Undead Rogue (Durotan)