I've been tanking with my cleric for a while now. I went a little unconventional and put 26pts in Shaman to get the battle charge and Strike of the Maelstrom. SotM is excellent, as it is a 360 degree ability. Ill often throw my Glacial Shield up, charge in, position myself so I'm within range of all mobs and use SotM then continue to spam my AOE macro.
You must have your Perceipt of Refuge up at all times (+20% block is huge mitigation potential). I macro it so that it never falls off, as long as I have convictions. I also macro Perceipt of Refuge, SotM and Even Justice, which is what I'm spamming the majority of the time during trash pulls. Make sure you manage your mana and regen when you need. Shaman's Endless Winter and a point in Justicar's Commitment allows me to stay near full practically all the time - I'll use Purpose on rare occasion.
- This is a big one - use Burning Powerstones on your weapon, they give you 200 spell power, which means a higher attackpower, block, parry, and dodge
- Run with Strength of the Bear (Shaman), as it gives you the most mitigation (block)
- Get your source engine filled with end game essences (at level 50 that is)
- If you rush into battle (you already have convictions for Perceipt of Refuge), do so with Glacial Shield on, as it causes damage back to attackers, as short lived as that may be.
- The trinket Akyron's mirror (spelling?) that drops from the water raid rift is fantastic, especially when coupled with a high block %. SHoE is also good
- LOS (line of sight) groups when you can, this will make pulls much smoother - just make sure no one does anything til you have aggro. As cleric, you lack a lot of taunts, and don't have a yoink like Seargent's Order (until Rebuke, if you go that far up, but that only works within 7meters anyway)
- Use your CDs often, especially Just Defense, it'll be back up before you know it
- Use your shields at the beginning of pulls, when you may not yet have the conviction for Perceipt of Refuge
- Make sure you don't have any HOTs on you before pulling, as they'll run right by you and facerape your healer...
- Use Purifier or Sentinal for your 3rd soul, the extra shield is great to have and the heal from Sent is decent aoe threat
- Don't be afraid to stop hitting (long as you have aggro) and spam a few self or group heals - as little as they may help they can be a life saver for a party member
- Be careful when using your battle rez so that they don't just end up getting cleaved right away ;)
Hope this helps!