Everyone does it different, but I use "heal who is getting beaten on" types of heals. I use(d) round-robin heals if I have multiple healers so it shares the healing duties across multiple people. It saves mana and means if the one person that could heal is CC or dead, you can still heal. The round-robin-ness is VERY limited at the beginning (< lvl you get BoK), but not much we can do about that, Blizzard broke empty parts in castsequences. I wish I could blame the people that used /click castsequences with like 40 commas in them, but everyone here would hate me.

heal a friendly or the person getting beaten on:
/cast [@focus-target, help] HealSpell
/cast [@focus-target-target] HealSpell

Old way to do round-robin: (don't focus on this, it won't work) (used 2 pallies at once, since flash is so small)
pally 1) /castsequence [@focus-target-target] reset=6 Flash of Light, , ,
pally 2) /castsequence [@focus-target-target] reset=6 , Flash of Light, ,
pally 3) /castsequence [@focus-target-target] reset=6 Flash of Light, , ,
pally 4) /castsequence [@focus-target-target] reset=6 , Flash of Light, ,

Now at low levels, you don't have many fillers, but that is the goal. You can't use empty spaces in castsequences anymore, so you have to put in spells that are tiny and crappy. Like BoK.
pally 2) /castsequence [@focus-target-target] reset=6 Blessing of Kings, Flash of Light,
pally 3) /castsequence [@focus-target-target] reset=6 Flash of Light, Blessing of Kings,

Sorry I can't help with in-game round-robins since they were taken away. You can try to use your broadcasting software to do them. That is probably how most people are moving to now.