You're in a good spot to pick up tanking again. If you start tanking regular Northrend dungeons at 70 with the full Cobalt set and a proper Prot spec (no more hybrids), you'll be armored enough to not feel squishy, and you'll quickly augment that with tank gear blues from the dungeons as well.

If you have gold, I'd suggest powerleveling Engineering as well for the ilvl 200 epic tank goggles available at lvl 72 and the +885 armor enchant to gloves (and the fun toys like bombs, hand rockets, nitro boots, etc.).

Other than that, be extremely aggressive in attacking mobs. Warbringer is New Hotness, use it. Some addons like Tidy Plates: Threat Plates and Omen or Skada threat meters are indispensable.

One last thing - when you tank Old Kingdom, always kill the Spell Flingers first. In heroic mode their Shadow Blast spell (6s cast) takes 80% of your hp (50% in regular mode). Save your interupts for that. They're probably the leading cause of trash wipes in all the 5mans.