Being one of the three priest classes one of our responsibilities is to assist heal. This is a short tutorial on how to do this as efficiently as I know how. If anyone would like to add to or modify this just post below.
Requirements:
Target Next NPC Key Bound
By default your Target Next NPC Key is not bound to a key on your keyboard. You need to set this in order to use this technique. You bind the key under your options menu under the key mapping section. I use the "," (comma) key for Target Next NPC, but you can use whatever you feel is convenient. Pressing this key will target the mob that is the next furthest away from the one you currently have targeted (in front) relative to yourself. Once it reaches the furthest away, the next press will cycle back to the closest mob. I suggest you go find a clump of non-agro mobs somewhere and hit this key a bunch of times to get a feel for how it works.
Generic Assist Hotekey
Create a social with the text "/assist" in it. Put it in an easily accessable bank somewhere where. The /assist command switches your target, to the target of your target. Said another way, the /assist command will allow you to target whatever is currently in your Health of Target's Target box. This is a great hotkey to have anyway, but we'll put it to special use in a second.
Health of Target's Target (HoTT)
This is a group/raid leader ability that allows you to see the health of your target's target. For example, if you target the Boss mob in front of you. Your Health of Target's Target box will show you the health of the Player currently Tanking that mob.
So, those three things are the key to assist healing. Here is how I do it.
Multiple Mob Assist Healing Flow
I use this pattern to assist heal while we're moving around, or when we have mutltiple adds in camp on boss events. This allows you to cycle around the available targets and see who needs heals and doesn't. If there are tanks in HoTT that are over 75pct health and appear to be getting heals, I usually move on to the next target. If I ever see a caster or DPS class in HoTT I usually consider them high risk and go ahead and assist heal regardless of their current health.
Boss Mob Assist Healing
I use this pattern when the main tank dies, during a tank change, or any time agro is bouncing around on a hard hitting mob. The idea is to wait for someone who can take the pounding to show up on HoTT and then get them heals as quickly as possible. Don't even bother with assist healing casters/dps in these instances, 90pct or more of the time they are dead before your heal will land, and the other 10pct they are dead before your second heal will land. Wait for the big boys to show up and take the pounding. I'll often use my AA heal Union of Spirits on these occasions becuse it is instant cast 3k heal and puts a big heal over time on the tank that stacks with everything else. I'll follow with Ancient heal, and while my gems refresh I'll usually click either my Tacvi spear or my PoR BP for maximum heal per second. The idea is to keep someone alive long enough for the clerics to get back into a rytthm and prevent a total whipe.