I’ve written up some encounter-specific tips as a blog post first, but this will probably be merged into the Holy Paladin guide at some point as well. At the time of writing this, our guild is working on Mythic Mannoroth so my knowledge of the Mythic version of the Archimonde encounter is somewhat limited by the fact that I haven’t actually done it. I’ll probably update that section once we get to it, though at that point it will probably be part of the guide and updated there.
First off, this post includes tips for healing each boss in Hellfire Citdadel and not an encounter guide per se. If you are unfamiliar with the fights themselves, I suggest visiting the Wowhead Hellfire Citadel Guides written by Dayani, or watching the Proper Bird video guides on YouTube for more general information about each encounter.