Tips:

1. Keep up sacred shield
2. Strafe Sideways so you are not letting the mobs hit your back
3. Bubble heal when you get low
4. Get the lowbies to heal you if possible
5. In the lowbie instances strip off anything that can lose durability and use a vendor shield
6. Keep up divine plea

Your aura will depend on what you are doing. If you are pulling the whole instance and running back to the alts you want to use devo so you dont kill any mobs before the get back into range of your alts.

If your alts are close enough that you can kill on the move then its ok to use Ret aura. Ive said it a few times that I really love Seal of Command for Aoe/trash.

Talents wise Divinity is widely recognised as not very good so I would swap those points out (though to be fair this talent is better for heroics than raids until you outgear the instance) Reckoning is usually a bad choice but for trash and Powerleveling it should be good. Ive said it a few times that I really love Seal of Command for Aoe/trash