Let's start with the basics

Stat Priority

People tend to overthink secondary stats a lot when choosing gear. It's important to remember that item level is always king due to how strong main stat is. 9 times out of 10 you should be choosing your highest item level gear, regardless of what secondary stats it has. My rough rule for Leech/Avoidance/Sockets is that they're generally worth ~6 item levels. Below you'll find a breakdown of our stat priority for Mythic+ and raid. *PLEASE NOTE: Crit is prioritized higher than every stat except Haste when playing the Lightforged Avenger build.

Mythic+ Stat Priority
Intellect
Haste
Crit Strike / Versatility
Mastery
Main stat is incredibly strong this expansion and continues to be the dominant choice when gearing. This is unlikely to change for the rest of The War Within so make sure you're focusing on item level first!
Haste is our best and most important secondary stat as you need a base level of Haste for this spec to play well due to the cooldowns on our core rotational abilities and reliance on Holy Power generation. There are no haste breakpoints for Hpal, but higher haste means more mana strains so I recommend staying around 23-28% for this first season.
Crit lost some value due to our lessened need for hard casting in TWW, but still provides good throughput, mana efficiency and spot healing. Versatility is another great stat for Mythic+ as it increases both our throughput AND our damage reduction, which is vital for pushing keys. You'll want to get as high as you can with your these stats after reaching a solid haste level.
If you just want raw healing throughput, Mastery is your best choice, but not by a significant margin. Remember it also has no effect on our damage, which in Mythic+ is a significant part of what we do. It's a much better stat now with the return of the Beacon of the Lightbringer talent, but in general is still the weakest M+ stat.
Raid Stat Priority
Intellect
Haste
Mastery
Crit Strike / Versatility
Just like Mythic+, main stat is by far the most dominant choice when gearing, even moreso than Mythic+ because in raid there is no such thing as a bad secondary stat. Prioritize leveling up your gear before worrying about optimizing secondaries.
Haste remains one of our strongest stats in all content, taking priority even over everything until you have at least 20%. Just like Mythic+, I recommend sitting somewhere in the range of 23-28% so the spec plays well but you don't strain your mana too much.
Mastery is a fantastic stat for raw healing power, especially with the return of Beacon of the Lightbringer, but it still takes a slight backseat to Haste even in raid. Use this as your stacking stat once you've hit your desired Haste levels.
Crit continues to be a strong secondary in state, even if it's slightly behind Mastery for throughput. Versatility is a solid throughput stat in raid as it will give you more healing, damage and survivability.
Cyrce's Circlet
Cyrce's Circlet is the new ring from the Siren Isles introduced in patch 11.0.7. There are many different gems you can equip, here I'll be covering the two best ring builds for healing and damage.
Best for Mythic+ & Progression Raiding
Your spells have a chance to proc a random effect at 150% effectiveness
This gem grants you a random effect from any possible citrine gem effects, which means it's very RNG as to how it contributes throughput. However, the proc rate is so high and it feedback loops well off of war queens and other groupwide effects that it's definitely the strongest option for your m+ or raid team overall.
Grants 1800 Mastery and increases Citrine effects based on Mastery
Fathomdweller's is fantastic for healing power, and increases the strength of all our other gem effects which makes it our best option for overall throughput (even in M+ where we don't stack mastery)
Grants 650 of every secondary stat
Stormbringer's is BIS for mostly everyone due to the raw strength of all the stats it provides. The only time you'd replace this is if you're running a purely damage oriented build.
Best for Pure HPS (Raid Parsing)
Your spells have a chance to place a HoT on 5 nearby allies
For raid healing parses, using the raw hps gems will likely provide the most healing, although it will be at the cost of you and your groups damage. There's no need to track this, just enjoy the free passive healing boost.
Your spells have a chance to heal up to 3 nearby allies
Same as the Old Salt's Bardic Citrine, Mariner's is the other raw hps gem that you can run for pure healing at the cost of you and your groups damage. There's no need to track this, just enjoy the free passive healing boost
Grants 650 of every secondary stat
Just like the best progression build lineup, Stormbringer's still makes the cut in the pure healing build as it provides so much raw player power from stats.
Best for Damage
Your spells have a chance to proc a random effect at 150% effectiveness
This gem grants you a random effect from any possible citrine gem effects, which means it's very RNG as to how it contributes throughput. However, the proc rate is so high and it feedback loops well off of war queens and other groupwide effects that it's definitely the strongest option for your m+ or raid team overall.
Your spells have a chance to deal damage to up to 3 nearby enemies
When it comes to healer damage, scaling our OWN power has always been the least effective for maximizing dps. Raw damage procs are almost always better, so it should come as no surprise we want the raw damage gems if we're going for the best possible dps options.
Your spells have a chance to deal damage to your target
When it comes to healer damage, scaling our OWN power has always been the least effective for maximizing dps. Raw damage procs are almost always better, so it should come as no surprise we want the raw damage gems if we're going for the best possible dps options.
Nerub-ar Palace Tier Set

For the first season of The War Within, Nerub'ar Palace is bringing us a tier set that amps up our Holy Shock, Word of Glory, and Light of Dawn healing:

2 Set: Holy Shock's healing is increased by 10% and its cooldown is reduced by 10%.

4 Set: Holy Shock increases the initial healing of your next Word of Glory or Light of Dawn by 8%, stacking up to 4 times.

This tier set will have very little impact on our playstyle, as most first season tier sets often do, allowing us to enjoyed a boost in throughput while focusing on learning all the new hero talents and changes to our core kit. Remember that your first spender after Divine Toll will always hit very hard since it brings you to full stacks. It's more important than ever to dump your Holy Power both before and after pressing Divine Toll so you don't waste your tier set.

Best Embellishments
Embellishments are a relatively small increase to your throughput, so don't stress too much over them. Below is a list of our best embellishments and which ones you should prioritize dependent on the content you're doing. For a chart of ALL embellishment values, check out QELive values and toggle between Raid or Dungeon on the top right of the header dependent on which list you're interested in seeing.
Best for Mythic+
Your spells have a chance to proc bonus stats for allies
While this won't provide much healing, it will bring significantly more damage than any other embellishment by a large margin so it's a fantastic pickup for Mythic+. None of the more healing focused embellishments will have a significant enough impact on your healing in keys to warrant running (the good ones we use in raid drop stacks out of combat, making it bad for dungeons).
Your heals amplify an allies gemstones
Similar to Binding of Binding, this is also focused on buffing your dps friends instead of yourself, and is only slightly behind the ring for damage in keys. Once again I do not recommend a healing focused embellishment as none of them contribute a meaningful amount of healing in Mythic+.
Best for Raid
Gain a stacking secondary stat while staying in combat
Ascension is our best option for raw throughput in raid, gaining stacks the longer you're in combat. This means that fights with heavy damage output early on won't see as much value as longer fights, but regardless of fight length this should always be your best option for throughput. I highly recommend crafting this on a weapon as your first embellishment of the season.
Doubles the effects of your Ascension embellishment
This embellishment doubles the value of your Darkmoon Sigil: Ascension embellishment, so throw this on one of your armor slots and enjoy doubling your weapon embellishment value!
Best Trinkets
Below is a list of the best trinkets you can get in the first season of The War Within, as well as the most powerful trinket combos for each content type. As it is early in the tier, make sure to check back here for updates to trinket lists if tuning happens. For a chart of ALL trinket values, check out QELive values and toggle between Raid or Dungeon on the top right of the header dependent on which list you're interested in seeing.
Best for M+ Pugging
Drops from: Grim Batol (Forgemaster Throngus)
Main stat proc
This trinket has proven to be by far our best trinket in all situations. The only caviat is that you have to run the Righteous Judgment talent as Lightsmith in order to maintain full uptime on the trinket as it only procs for Lightsmith via consecration.
Drops from: Mists (Ingra Maloch)
Secondary stat proc based on food buff
Unbound Changeling has always been a top tier trinket and will continue to be with its return this season. There's not much to think about with this trinket other than which stat you want it to proc, as that will be based on your food buff. I recommend Haste, but you can also opt for Crit/Mastery if your gear has too much haste baseline.
Best for M+ Pushing
Drops from: Grim Batol (Forgemaster Throngus)
Main stat proc
This is insanely strong for M+ pugging and pushing alike, it's out best trinket by a decent margin and you should prioritize taking this if you get one in your vault over anything else. Otherwise enjoy grinding Grim Batol for hours ;)
Drops from: Mists (Ingra Maloch)
Secondary stat proc based on food buff
Pushing keys has always been about fast reaction times and quick heals so haste proc will for sure be the way to go, regardless of your base haste levels. Don't worry about tracking the proc, just enjoy the free haste when it does!
Best for Raid
Drops from: Grim Batol (Forgemaster Throngus)
Main stat proc (Herald of the Sun ONLY)
Similar to Mythic+, you should only run this trinket if you're playing Herald of the Sun due to its interactions with HoTs/DoTs. If you are playing Lightsmith in raid for any reason, you should run Unbound Changeling instead.
Drops from: The Dawnbreaker (Anub'ikkaj)
Random secondary stat proc
This is as simple as a stat stick as you'll see in modern WoW. Don't overthink it much just throw it on and enjoy the free throughput! Generally better in raid compared to Mythic+ since it can proc Mastery, which is less desired in dungeons.
Other Trinket Options
Drops from: Ara-Kara (Avanoxx)
Abilities have a chance to give you Intellect and deal damage
Sacbrood is a fantastic alternative to our BIS trinkets. If you're struggling to get your hands on a Gale of Shadows/Changeling or you get a big Sacbrood in the vault, it's a great pickup.
Drops from: Nerub-ar Palace (Anub'arash)
Stacks Intellect, 20s On Use: Consume stacks for big Int buff
This trinket is fairly strong in raid as it provides a lot of mastery and main stat. It can be a little awkward to use, but line it up with wings for a huge boost to your cooldown window! In general this should never be taken in Mythic+ as it's main stat mastery which is by far our least valuable secondary in Mythic+.
Drops from: Nerub-ar Palace (Bloodbound Horror)
1m 30s Use: Redirect 20% of healing until full, then release
Creeping Coagulum can be a little awkward to get used to, but can actually provide a decent amount of damage if you use it for overhealing. That's because when you release the stored healing, it gives players damage procs based on the amount of overhealing. Overall, not quite as good of an option as the meta trinkets listed above but definitely strong in niche situations.
Drops from: City of Threads (The Coaglamation)
Store overhealing. 1m Use: Shield ally based on stored healing
In theory, converting your overhealing to a usable shield on a one minute cooldown seems pretty great for pushing keys, but the tuning on the trinket is a bit low. This may end up being a meta trinket if it gets buffed so keep an eye out for trinket tuning!
Drops from: The Stonevault (Speaker Brokk)
Spells have a chance to proc a shield on an ally
This is a relatively mid trinket but isn't bad for early on for raw throughput. It does increase effective health, but not realiably as you have no control over the procs so overall probably won't see much use in the end game.
Drops from: City of Threads (Izo)
Spells have a chance to enhance an ally
This is a trinket to keep an eye on early in the season. It provides some unique buffs to allies including main stat, secondary, tertiary, damage and healing procs. I could see this being a trinket that could break into the meta if cheese strats are found to force the stronger buffs to proc but that's something we'll have to wait and see what people discover.
Drops from: Nerub-ar Palace (Broodtwister Ovi'nax)
Build stacks by standing still. 2m Use: Suspend stacks
While this is one of our higher raw throughput trinkets, it requires STANDING STILL, which I don't know about you but is basically impossible for me as a melee healer. Not just because of dodging mechanics and the motion of Mythic+ in general, but also because I subconsciously strafe 24/7 so this trinket is a no go for me. But if you're feeling extra stoic give it a shot.
Enchants and Consumables

With The War Within you'll see the return of many familiar enchants, oils and armor kits as well as interesting new ones! Before every dungeon or raid boss you'll need to make sure you have everything reapplied to your armor so I suggest getting a weakaura like this as a reminder.

Item Enchants
Chance to increase your Intellect or heal nearby allies
Radiant Power will generally be your best option for Mythic+ while Fiery Resolve will be the go to raid enchant. If you want one that works for both content types I'd suggest Radiant Power as Fiery Resolve loses a lot of value in Mythic+ but Radiant Power is still fairly good in raid.
Increases your Intellect by 745
Not much to see here, main stat is king as always so don't worry about the mana enchant option.
Increase your Haste by 315 / Versatility by 390 (-110 Mastery)
Your default for raid should always be Radiant Haste (or crit depending on your gear), but in Mythic+ I recommend Cursed Versatility as you can gain more desirable stats at the cost of Mastery which has very low value in dungeons.
Increase your Leech by 1020
Leech has always been our strongest throughput tertiary stat so your default cloak enchant should be Leeching Fangs, only swapping to Avoidance in very high keys if you need it to survive one shot mechanics.
Armored Leech (Bracers)
Increase your Leech by 2040
For the same reasons you want Leeching Fangs for your cloak, you'll want Armored Leech for your bracers in most cases.
Increase your Stamina by 131
Boot enchants are never very interesting, enjoy your free Stamina!
Increases your Intellect by 747 and Stamina by 230
In most cases having the increased health pool is always better so you'll default to this but if you ever find yourself running into significant mana issues you can try Daybreak Spellthread.
Weapon Runes & Gems
Increases your Crit and Haste by 155 for 2 hours
This expansions weapon oil happens to provide us with two very strong secondary stats so make sure you stock up! This will need to be reapplied every hour. Note: If you are playing Lightsmith, you should run Rite of Sanctification instead (you unfortauntely can't use both).
Increases Intellect by 181 and Movespeed per gem
As our main unique gem, it should come as no surprise we want more mobility! Reminder to equip at least one of each type of gem (sapphire, ruby, onyx and emerald) to get full value from this.
Increases Haste by 147 and Crit by 49
This is just our basic filler gem, change this out if you want more Haste/Vers/Mastery instead.
Phials & Food
Increases your Crit / Haste by 3323
Depending on which one your gear is lacking in more, you'll want to run either the Haste flask or the Crit flask.
Increases your Intellect by 445
If you have luxurious friends they may bestow upon you a grand feast, which is by far our best option for food. But for the common folk, we must dine on Jester's Board instead.
Increases your highest secondary stat by 445
This is the main personal food of The War Within, providing a large amount of secondary stat. If you don't have rich friends throwing feasts at you this will be your bread and butter.
Potions
Increases 3 Secondary Stats by 2617 for 30 seconds
Tempered Potion is the main throughput option this season but it's a bit different from previous expansions. Instead of granting main stat, it grants three secondary stats instead.
Instantly restores 4,000,000 health
As always, make sure you use your healing potions whenever you're in danger. You'll find these potions to be extremely strong self healing and off the GCD.
Restores 375,000 mana over 10 seconds (channeled)
In raid this should be your go to mana potion as it restores more than the regular one. Make sure you find a safe time and place to drink as you can't move once you start channeling!
Instantly restores 270,000 mana
This is the standard mana potion we get every expansion. Great for if you're in a pinch and need mana quickly and there's no time or safe spot to drink a Slumbering Soul Serum.
Increases up to 5 allies Intellect by 632
For my min/maxer friends, this is a unique potion that you can use right before the start of a key as your team will keep the main stat and you can use your personal pot while it's still active.
That's it for character setup, now it's time to dive into the playstyle of Holy Paladin.