What you can do beforehand
Buy glyphs in advance. The prices of glyphs are going to skyrocket when the new patch comes out, as every scribe tries to make some scratch off of the new demand of returning and unprepared players. You can mitigate this a bit by buying today all the glyphs on live that will be converted to the new glyphs come 5.0.4. Here's a great list. Just scroll down to the paladin portion. If you're wondering which glyphs will be worth it in 5.0.4, check out the glyphs section of my Mists Protection 101 guide.
Stock up on purple gems. As I detailed in my 101 guide, it's going to be really important to hit and expertise cap, and one of the ways you can make that easier for yourself is to cover some of that expertise requirement with gems. While hit rating is blue, the same color as stamina, and thus not really worth it -- expertise is our weakest gem color, red.
With our choices for red being either a purple gem with parry and stamina, or expertise and stamina, and sims showing expertise being worth more survivability than parry, it's a no-brainer choice. We can cram those red sockets with Guardian gems and lessen the burden that we need to make up with reforging. (More on that in a bit.)
First thing, day one: Hit the reforger
Time for a very expensive visit to the reforger! Goal number one will be to cap hit and expertise, to get the most from your active mitigation and to guarantee a steady, dependable holy power generation rate. You'll need 769 hit rating and 769 expertise rating to cap melee hit and spell hit and to soft-cap expertise. You can mitigate these numbers with Guardian gems or your various racials; for example, a human would only need 667 expertise rating with a Souldrinker equipped.
To make this process less brain-asplode, I recommend using Wowreforge.com to calculate out your reforging for you.
Get an idea of how active mitigation works
Remember, the single biggest change to our playstyle in 5.0.4 is the introduction of active mitigation. Tanking now is more than just passive avoiding or mitigating damage and sparingly using cooldowns when various things hit various fans. Now our playstyle builds on the example of the new Holy Shield we've been playing with for a year now -- hitting buttons regularly for short-term boosts in survivability.
The way we'll be handling our stable of active mitigation abilities -- Shield of the Righteous and Word of Glory -- won't really be hard to pick up. Stack holy power through our various generator abilities (same abilities that built HP in Cataclysm, with the addition of Judgment now) and then when you have 5 holy power, use Shield of the Righteous. Keep in mind that ShoR is now off the global cooldown, so you can immediately hit that button as soon as you have 5 holy power without stuttering your rotation.
Note that there is some value to be had delaying your ShoR for a moment if a big, predictable physical hit is coming, so that you apply the 30% damage reduction to that hit, rather than a weaker one three seconds before. But that's something that you'll want to practice.
As you use Shield of the Righteous, you'll be stacking a self-buff called Bastion of Glory, which improves your Word of Glory by 10% for each stack, capping at five. Word of Glory should be used reflexively once you've taken a big hit and need to immediate top yourself off. Do note the overheal bubble is gone now, so there's no benefit to "stacking the deck" in advance of a massive hit with a WoG.
Practice your new rotation on a target dummy
Again, I won't steal all the thunder from the Mists Protection 101 guide (seriously, it's huge -- read it!), but your rotation starting on Tuesday will not be unrecognizable from what you're working with now. Instead of using one filler between Crusader Strikes/Hammers of the Righteous, we'll use two. Likewise, the relative position of each filler in our ability priority remains the same, with the addition of the new level 90 talent/attack taking priority over Consecration and Holy Wrath.
As such, I don't think it'll be too hard to adapt. Just remember that Shield of the Righteous is off the global cooldown now, so you don't need to wait to use it once you have 5 holy power. That'll be key. Moreover, remember that you'll want to use Hammer of the Righteous even on single targets so you can apply the Weakened Blows debuff -- that'll be key.
In all my various pre-Mists posts, I've neglected mentioning Blinding Light. It's our level 87 spell, and it's just a crowd control spell. Kind of underwhelming, especially compared to what other classes are getting, but it will still be handy for tanking.
Don't panic when you can't find Exorcism anymore. It's been made to a ret-only spell. However, in the divorce, we got sole custody of Consecration and Holy Wrath, so that's something.
If you're looking to swap seals, check your auras bar. Auras are gone and their bar was taken over by our various seal spells.
Make sure to have Devotion Aura, our new raid cooldown, somewhere handy. Very key for group play!
Good luck with the big transition on Tuesday! May all your addons miraculously work and all your mitigation strike true.
The Light and How to Swing It shows paladin tanks how to take on the dark times brought by Cataclysm. Try out our four tips for upping your combat table coverage, find out how to increase threat without sacrificing survivability, and learn how to manage the latest version of Holy Shield.