Simple fast upgrade:
-enchant your gear
-reforge max to spirit and then to mastery
-change talent selfless healer to eternal flame
-change talent Execution Sentence to Light's Hammer
-take glyph of divinity - give a lot of mana when use lay of hand
We have a lot more aoe than just holy radiance
-Light's Hammer - cheap strong healing - but people need to be stacked
-LOD - no mana cost
-holy avenger - just generate holy power with holy shock or crusader or holy radiance and spend LOD every time - big strong heal even when people are not stacked
-eternal flame - if you know that big dmg is coming just try to put eternal flame on as many you can with 1 holy power each and when aoe start you will have less to heal
-after holy radiance ypu will got passive daybreak that make holy shock also heal aoe, so always holy radiance then holy shock
When you got mana problem
-use potion of focus during fight - wait for time where is no dmg and call it to other healer
-use divine plea on cd
-geam pure spirit
-use spirit enachant on chest
-use spirit flask and food
-gear more, go arena for free items 483
Read guides on forum, check world of logs, watch few movies on youtube.