This "trick" may not be around for long as it makes Clerics and any class capable of proccing heals pretty much invincible and able to solo most mobs in the game including elites.
First things first, get to a Rare Planar Goods (not a regular planar goods npc) vendor and pick up a Planar Essence that procs on heals.
There should be one of these in each zone.
The cost should bet a purple zone sourceshard and a lot of planarite. For example, the Stonefield one is called Gleaming Stone Seed.
Once equipped in a greater planar slot, it causes your heals to have a chance to proc a 300 hp heal over 8 seconds.
The trick here is it is supposed to heal 300 health total over 8 seconds.
Now you're thinking "why does this matter? You are dumb"
It is here where I say "NO U" because the Justicar tree has an ability called Salvation that heals you for damage done. It counts as a casted heal and it procs this ability from the greater planar essence. So while smashing faces around, you're getting sweet 2400 heals.
Wait, did I say 2400? Yes. The item is bugged so that instead of providing 300 healing over 8 seconds, it gives 300 healing every second for 8! 2400 hp heals total!
So what's the best way to take advantage of this? Try this build on for size:
Soul Tree Calculator: Shaman (31) / Justicar (11) / Druid (0) :: Rift: Planes of Telara :: ZAM
The shaman tree naturally does a lot of damage (which is good because Salvation healing is based on damage done) and also has a talent that increases healing received! Justicar gives you some 5% extra damage, a ranged attack, as well as the important Salvation healing and boosts for it. The third tree is kind of useless but the Fearie healing gets the buff as well, so yeah.
Grab the Freemarch trinket that procs heals for an added boost/hilarity.