Icy Veins and Wowhead guides are usually good starting point.
Icy Vein's guides are a bit messy, but provide solid information as well as explanation of why/when/how.
Ultimately, as above post said, best option is Discord.
In case that you need it, here's a list of all discord channels for all classes.
Code:
Death Knight: https://discord.gg/acherus
Russian Death Knights : https://discord.gg/QktwJdq
Druid: https://discord.gg/0dWu0WkuetF87H9H
Hunter: https://discord.gg/HxV3TR5
Mage: https://discord.gg/0gLMHikX2aZ23VdA
Monk: https://discord.gg/0dkfBMAxzTkWj21F
Paladin: https://discord.gg/hammerofwrath
Priest: https://discord.gg/WarcraftPriests
Rogue: https://discord.gg/0h08tydxoNi7DSNe
Shaman: https://discord.gg/earthshrine
Warlock: https://discord.gg/0onXDymd9Wpc2CEu
Warrior: https://discord.gg/Skyhold
Demon Hunter : https://discord.gg/zGGkNGC