Armor reduces damage taken. Priests, so long as they can survive long enough to do so, can repair the damage. Just roll with the punches. And the bonus from Inner Fire does make a difference...just not much when you only go from 10% mitigation to 20, and you don't have many HP to start with.
1) Shield yourself before a fight. This is a limited strategy, but one some people swear by.
2) Keep renew going. You're taking damage as time goes on. Why not also regain health as time goes on? It's an instant cast spell, which is very handy.
3) Simply heal yourself. Casting a flash heal mid-fight doesn't always work real well, but there are talents that make this easier, such as Focused Casting and Improved Flash Heal.
4) Psychic Scream. This has very limited use, but it can be helpful to get two free casts off on your target. Very useful for Mind Flay (or, I imagine, Starshards.) Can also give you the break you need to cast a heal if you couldn't manage it before.
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Only the exceptions can be exceptional.