All of the advice I have seen here has been solid. The only other thing I would add is how to deal with swaps. Even well geared tanks can get ripped off of if the original tank has full stacks of vengeance, especially if they are using DPS trinkets that have proc'd at the time of the swap. Using Hand of Salvation on the other tank is a great way to give you a chance to grab aggro and build up a little vengeance while the other tanks vengeance is wearing off and can really smooth out tank swaps. I personally use a hand of salv mouse over macro for this.
Another thing you can do is use an offensive CD like Avenging Wrath or Holy Avenger to increase your threat when you are taking the boss. Obviously you don't want to waste this CD so make sure you know the fight and map out the fight and only use it if you know that it will be back up for a burn phase.