- Make sure Righteous Fury is always up. Because Ret has extra threat reduction from Fanaticism, keeping RF up is crucial. I refresh RF if it goes below 10 minutes.
- Wear Protection Armor and a high-DPS 1-hander. Stamina, Defense, and Strength are your key stats. I've found that good tanking gear usually comes from instances, though there is a little bit as quest rewards. There are also some decent crafted pieces.
- Pulling can be hard. Pull with Repentance if you can. Otherwise body-pull if it is safe, or get another class to pull for you, and drop a Consecration to pick up the mobs.
- I prefer using Seal of Vengeance as you can switch targets while the Vengeance stack ticks away. You'll have to switch targets a bit more often than Protection.
- Ability preference is something like: Consecration, Judgement, Divine Storm, Crusade. Emphasis on Holy damage that can hit multiple targets.
- Don't forget about Divine Protection. It's really powerful now for reducing damage at crucial points, especially early on large pulls, where you have multiple mobs beating on you.
- Righteous Defense is actually pretty useful with the new threat display. As soon as one of your teammates highlights in red, you can select them and RD. You don't have to find the mob that is actually attacking them. This is invaluable on larger, more chaotic pulls.
- Unlike Protection, a lot of your threat comes from active abilities, not reactive abilities. As well, you have Judgements of the Wise, so you don't need healing to regenerate mana through Spiritual Attunement. This means that you and your teammates can use stuns liberally, and still maintain high levels of threat.
Realistically, tanking as Retribution is not a whole lot different than tanking as Protection for 5-mans. Make sure your healer knows that you might be a bit squishier than normal so she is prepared. Tab around a bit more to maintain threat on multiple mobs. Stun early, stun often.
I personally wouldn't advertise myself as a tank. But I would offer it as an option if the group is having trouble finding one.