Tanking on the paw just means standing on one of his two front paws, since, like Wyrm breath attacks, he has Sulfurous Breath, which is frontal cone. If you attack him standing on one of his front paws, it'll lower the damage you take from that attack. If you've ever fought a Wyrm before, then you know the concept, but if you haven't before, here's an idea of it. I whipped this together real quick to give you an idea of where you want to stand, with either position being shown.
You basically want to be on one of his two front paws, close enough so that he won't turn towards you when he goes to attack you, and instead strikes at you with the paw you're standing on, or biting at you with the head closest to your position.
For Lava Spit, really your only way of handling it is to have a good -MDT set, some Fire resistance, and/or Shell. Did he happen to do his howling animation before he did that Lava Spit? From what I've seen, his howl will act as a sort of Boost for the magic spell or TP move he does after it. It doesn't affect Addle or Ululation, but if it's a damaging attack, it'll do far more damage than it would normally, like it's an Attack/Magic Attack boost. If that's the case, once you see him howl, just prepare yourself for something right after. He'll always do a TP move or a spell right after the howl (which might end up being another howl), so if you swap over to -MDT/DT gear right as he finishes his howl, you might have a better chance to survive it.