NOTE: On current build, Dual resto is maintained for maximal healing. This is good for veteran and trials. On trials, substitute out Rapid Regeneration for Healing Springs. Radiant Oppression is a flex slot, and feel free to throw in something you like such as Purge. In high DPS groups, I slot Purge for the mana regeneration. Overall, your primary job is to heal/buff allies.

Weave: I run my back bar for mana regeneration. Spend 75%+ of your time on Bar 1 unless youre leveling back bar. Its your primary heals. Don't activate mage light it wastes mana, we slot it for the passive.

Points of authority: As a healer, feel free to leave a bad group. If someone dies it isn't always your fault. Sometimes bad DPS gets itself killed by standing in red. Or getting one shotted due to having low (<15k) HP. Or the tank loses agro. If the group sucks, just requeue. You, as the healer, are a commodity. Another group is always one click away.

GEAR: I recommend a set of Laws of Julianos and Sanctuary for god-mode heals. K's is OK as an alternative. SpellPower Cure is optimal, if you have it.

Keep these (active) buffs up constantly:

Extended Ritual (toughness, HoT)
Channeled Focus (healing buff, regen, toughness buff)
Combat Prayer (every 8 seconds as needed, its cheap enough)
Aggressive Warhorn

Run these heals as needed:

Breath of Life (It's your big Oh-SH** heal)
Rapid Regeneration (heal over time, refresh as needed)

Don't spam these:

-Breath of Life
-Buffs, just refresh as needed
-Radiant Aura, used to be good to activate, now its meh. Good mana restore, but only for magicka heavy DPS groups.
-Mystic Orbs. Synergy every 8 seconds. Use it sparingly, dont spam. With new radiant aura, this can be a flex slot or even removed.

Spare a second, sir?

Sometimes you have spare mana/time/both. Use a debuff. Or a damage over time. Radiant Oppression is our OP execute, it is included due to its sheer broken nature. I can assure you, it will be nerfed in future patches. As of the time of this writing, that hasnt yet happened. Consider it a FLEX spot, where Purge or others can be thrown in.

Use your Radiant Oppression if the DPS is struggling on that last 20%. But don't overdo it. Never use it above monster life 50% its a total mana hog. Also don't use it unless its a boss.

Throw out some Mystic Orbs. Sorcs love it, they get free mana back. No Sorcs? Throw down your Shards instead for the STAM.

Or, refresh those buffs like Combat Prayer. Or hit the boss with Power of the Light, it translates to roughly 10% damage taken on most bosses.

Morale of the story? Don't always spend mana just because you can, but definitely keep buffs up. If mana regen is sluggish then check your food/gear. I aim for 2500+ magicka regen with Atronach, Divines gear and Radiant Aura (this is a huge part of mana regeneration)
Healing Springs (TRIALS ONLY, have this running even at the cost of Combat Prayer going down. It hits so many people its sick. It can be spammed with relative comfort, but it wastes some mana if not enough targets).
**AVOID SPAM HEALING, ITS RARELY NEEDED. I cannot hit that point home enough. Its better to have mana and not need it than to need it and not have it.

Heal for FOOD: Run food, it's vital. Prefer magicka regen, ideally aim for +health and magicka regen. Usually can be bought cheaply enough (10-20 gold tops per use) from vendors. I personally use Orzorga's or Black Night Cordial. Note drinks don't stack with food, and vice versa. The mana regen helps a lot and should always be running. I recommend any of the numerous buff bar ESO UI addons for tracking this and other buffs.

Disclaimer: Some ESO players believe "healers should DPS". I am not one of those players. Most slotted DPS abilities are giving up theoretical healing potential. Breath of Life is included to have a panic button, for situations where HoTs and DoTs are just not cutting it.

Rotation:

Lay down your Buffs before combat, with at least Extended Ritual, Channel Focus and Combat Prayer. Then switch to Bar 1, lay down Rapid Regeneration as needed. Apply BoL in bad situations. Keep up Blazing Spears and Combat Prayer every 8 seconds. In most situations, you won't want to switch back to Bar 2 (Buff Bar) in mid combat. Longer fights are a notable exception...

While healing, do NOT ever spam Breath of Life. Do buff early and often. Prefer to use Rapid Regeneration and Healing Springs, if you must. HS is better in Trials. Breath of Life can be thought of as a panic heal. Throw in some damage when/if you can, for solo or group play. In dungeons, this build is better off using heavy attacks during down time to proc some of its passives related to magika regen.

As the party's defensive officer, never hesitate to tell people where to stand in encounters so that they survive. Never hesitate to ask another player if they have repaired recently or eaten their food for regeneration. As a healer, you want to prevent damage, and the best way to do that is with buffs and debuffs. Healing Ward, while not included in the default setup, is great for mitigating damage.

The purpose of this build is to buff, support and most importantly heal allies in a Dungeon or Trial setup. Dawn's Wrath -> Solar Prison is meant to be switched in for the Bar 1 Ultimate in situations where the stun and debuffs are preferable. This build is not setup to do any damage, save through the Blazing Spear, which is itself included to allow for STAM recovery for the tanks and melee DPS.

In some situations, Healing Ward might be substituted in to Bar 1 (healing) over Breath of Life or another ability. Running at least one HoT is very much considered mandatory, however. Rapid Regen is simply too cheap and too good not to use. If you absolutely must do damage, the recommended go-to skills are Puncturing Sweeps and Blazing Spear. Many of the choices on Bar 2 are buffs. You will want to periodically switch back to Bar 2 and rebuff your Extended Ritual and other buffs, as needed. How often you do so will be a function of party needs, your magicka regeneration and encounter length. It takes some getting used to. Combat Prayer is on Bar 1, because you want close to 100% up-time on it.

Why have all the buffs on one bar? Simple: It lets us stay on Bar 1 for healing. We switch to Bar 2 to either remove a status or to refresh buffs when they expire (use ESO UI mods to see buff timers). Extended Ritual should always be running and ideally Channel Focus as well, to maximize outgoing and incoming healing. Whenever possible throw down a Restoring Aura (bar 2). It helps your regeneration, and the STAM/HP/MAG regeneration of the entire group. 20% is a huge amount and can help the entire party. Combat Prayer is a great buff too for party DPS. Healing is about three things:

1) Healing damage. Of course. Mage Light helps maximize our Rapid Regen and Breath of Life heals, hence its on Bar 1 only.
2) Preventing damage. Through buffs and debuffs. Our primary debuff is Power of the Light which helps down enemies faster. Its on Bar 2, as are the other debuffs.
3) Buffs. A buffed party ends encounters quickly. Resource regeneration is a huge part of this build. STAM tanks benefit enormously from steady resource regeneration.

Is this a bold build? Yes, yes it is. It rejects entirely the notion that a healer should EVER waste a single point of his magicka on trying to do DPS, a viewpoint very much at odds with how this game works. So why not use Elemental Drain? Simple, it isn't worth using a Destructive Staff in order to use it. We're better off throwing our Resto abilities on 2 bars to maximize our support and healing, if we fulfill the full role of a support templar.

Leave the destructo staff at home, you're no wizard Harry. And you don't need to be! Healers are for healing, and sorcerers are for blasting. Let the DPS do its job, and enable them to do it.

OVERALL ADVICE:

1) Never overheal.
2) Know the encounters before hand whenever possible.
3) Keep your gear current.
4) Keep mag regen up, and try to keep Restoring Aura running. Swap in Healing Springs in trials healing. This build is a "Dungeon" and "General PvE" build. I don't play PvP or much care for it. So if you're looking for a PvP healer, youd likely take a few things out of Bar 2 and throw in some Alliance War skills and passives.

While leveling: Use things like your Tier 1 abilities in Dawn's and Aedric lines. Puncturing Sweeps is great for leveling. Swap it out eventually for Shards.. the lack of Repentance is felt by some STA tanks, so run your aura to make up for it.

CHAMPION POINTS

Blue

Since we focus mainly on healing in general, I do 100 into Blessed and 87 into Elfborn, super simple. Another option for a good split...

50 Elemental Expert, 50 Blessed, 28 Elfborn, 10 Spell Erosion, and 49 into Thaumaturge.

Red

I stick with the time tested 85 Hardy 85 Elemental Expert split, with 9 into Quick Recovery, 1 into Expert Defender, and 7 into Thick Skinned for a well rounded damage mitigation and nice boost to healing.

Green

I focus on capping out Magicka Cost Reduction and then dumping the rest into Regeneration. This ensures the best Magicka Sustain for DPS and healing.

VARIANT (FROST STAFF) for Solo PvE Content or for Damage alternative

Bar setup:

Ultimate: Solar Prison
1-Puncturing Sweeps (AoE Cleave)
2-Reflective Light (Direct Damage, AoE, spammer)
3-FLEX SLOT - Either Radiant Oppression OR Radiant Aura
4-Elemental Blockade (AoE DoT, debuff movement w/ chilled)
5-Inner Light (Mage Light, self-buff for 20+% crit buff)

Allows for massive AoE clearing, you don't even really *need* Radiant Oppression but it's a great option to have. I am content in saying this setup, combined with Combat Prayer on Bar 1, can easily solo all the content in the game including Maelstrom Arena. Between sky high crits through Mundus Stone Thief and Inner Light, DoTs and AoE galore, with self-heals in the 10,000+ rate, you're sitting pretty.