>bfa priest

addon manager:
https://www.twitch.tv/downloads (subscribe to ttv/ketzer95 for more free tips and tricks [former rank 1 unholy btw])

important addons (make sure to install through the twitch client icon so you can update them easily):
https://www.curseforge.com/wow/addons/details
https://www.curseforge.com/wow/addons/bagnon
https://www.curseforge.com/wow/addons/scrap
https://www.curseforge.com/wow/addons/raiderio
https://www.curseforge.com/wow/addons/method-dungeon-tools
https://www.curseforge.com/wow/addons/little-wigs
https://www.curseforge.com/wow/addons/big-wigs
https://www.curseforge.com/wow/addons/dejacharacterstats
https://www.curseforge.com/wow/addons/gtfo

Weakauras (Custom scripts/addons that give you a lot of personalized tools for your UI):
https://www.curseforge.com/wow/addons/weakauras-2

you can experiment with different strings and see what you like:
https://wago.io/weakauras/classes/priest

...

plenty of guides and info about what talents/azerite/essenses to run in places like icyveins but imo it's always best to see what other people playing your class are using. M+ and raids have a lot of revolving factors given there are a dozen different dungeons so there isn't always a cookie-cutter answer:
https://www.warcraftlogs.com/zone/rankings/20#class=Priest
https://www.warcraftlogs.com/character/us/zuljin/shrekisblack#partition=2