It was a fairly painless five levels that brought you to the top of the food chain in Pandaria, and, as the expression goes, now you can play the game. If you're officially leaping on the gear treadmill and getting ready for raiding, you have a lot of work ahead of you. Thankfully there is a lot to do, and easily available sources of gearing, so the task isn't particularly onerous. Before you know it, you'll be geared and ready to tank anything the sha toss at you.
Briefly, what kind of gear do you want?
I don't want to delve too deeply into this, because it's a whole 'nother column's worth of exposition, but when it comes to gearing I strongly recommend grabbing pieces that will emphasize a control style of tanking. That is, anything that boosts our active mitigation by making our holy power generator abilities hit, hit more often, and our active mitigation more powerful.
Specifically we're talking about first gearing to cap hit and hard cap expertise (yes, hard cap). Then go for haste and mastery in equal amounts. Reforge out of any avoidance you have to achieve these goals. As such, you'll want to go for gear which has hit, expertise, haste, and mastery -- and if you're lucky, avoid anything with dodge or parry (or worse, dodge and parry).
For the gritty details behind the "control" strategy, I strongly recommend this blog post by Theck. Now, that said, let's get down to brass tacks!