On Deathbringer Saurfang, he casts a spell call Rune of Blood, which debuffs his current tank. Any attacks that tank receives causes Saurfang to be healed. The other tank has to taunt IMMEDIATELY. You should be watching action timer bars from DBM or DXE or Bigwigs or whatever else you use to know exactly when it's casted, so you can taunt right away.
Also, set the other tank as your Focus target so you can see his debuffs.
On a fight like Lady Deathwhisper or Toravon the Ice Watcher, the current tank receives multiple "stacks" of a debuff, and you can see how many by the debuff tooltip on your focus target frame. When it gets too high, you need to taunt.
As a paladin, you have Hand of Reckoning, and Righteous Defense. Both taunt just as well, but you should probably use HoR first to get into the habit of it. You don't want to accidentally taunt more than just the one target on fights with adds.
Both of your taunts count as spells, and require 17% hit to always work on bosses. You'll almost always be fine with the standard 8% hit for melee (which is 10% or 11% for spells), but there's also the Glyph of Righteous Defense for another 8% hit for both of your taunts, giving them a 100% success rate if you're melee hit-capped.