Gear
Holy Paladin Onyx Annulet & Primordial Stones
The Onyx Annulet is a Ring that was introduced in Patch 10.0.7 that comes with three sockets that you can add unique gems (Primordial Stones) to, with different effects.
Right now the Onyx Annulet is by far the best option for damage and will outscale a 447 ilvl crafted Ring in 10.1, with the following gems:
Holy Paladin Tier Set
2-Set: Holy Shock’s critical strikes heal for 60% more and reduce the cooldown of Light's Hammer by 2sec, or Holy Prism by 1 sec.
4-Set: Light's Hammer heals 100% more frequently and generates 1 Holy Power every 4 sec. Holy Prism's healing is increased by 80% and it generates 1 Holy Power if cast on an enemy target, or 3 if cast on an ally.
Embellishments
For raiding, your best embellishments for a HPS perspective will be the Allied Wristguard of Companionship and Elemental Lariat. For a progress scenario, Undulating Sporecloak might be good for you. That being said, the biggest power spike generally would be crafting a Weapon if you don't already have a 447 one. In this case, you would play Healing Darts. If you have the Rashok Molten Heart trinket, then the Potion Absorption Inhibitor is good, assuming you use Intellect pots.
Mythic+/Damage focused
Shadowflame-Tempered Armor Patch is by far the best DPS Embellishment for Holy Paladin, and you would most likely run two of them in Mythic+. Keep in mind you can only use this embellishment on "Armor" pieces, such as Shield, Legs, or Chest.
Holy Paladin Trinkets
These are your best in slot Trinkets for 10.1:
Rashok's Molten Heart: Your healing spells have a chance to awaken the Heart, restoring 13,492 mana over 10 sec and causing your healing spells to restore 30,081 additional health over 10 sec. Overhealing from this effect invigorates your target, granting them up to 526 Versatility for 12 sec.
Screaming Black Dragonscale: Your attacks and abilities have a chance to grant you ephemeral dragon wings, increasing your Critical Strike by 902 and your Leech by 283 for 15 sec.
Neltharion’s Call to Chaos: Your area effect spells and abilities have a chance to grant you 2.443 Intellect and increase damage you receive by 5% for 18 sec.
Ominous Chromatic Essence: Resonate with the power of your sworn Dragonflight, granting you 598 secondary stat. Allies sworn to a different Dragonflight gain 66 secondary stat from your Resonance. You may only benefit from one Resonance per Flight.
Use: Attune with a nearby Dragonflight Oathstone in the Dragon Isles.
Cloak
Voice of the Silent Star: Whenever nearby allies take damage, the Voice has a chance to beckon you. Upon hearing it's call 10 times, you fully submit to its influence, stealing 132 of the 4 nearest allies' lowest secondary stat and giving you the stolen amount plus 1,979 to your highest secondary stat for 8 sec.