A general "When/what to use aetherflow on" as SCH:
-Sacred soil: Unavoidable damage that will hit multiple party members or as a last resort tank cooldown.
-Lustrate: Tank hits critical HP and might die before the next GCD finishes.
-Energy drain: When the other two aren't needed to regenerate MP and deal some damage.
Never let Aetherflow sit off of cooldown during a fight, try to aim for having 1 stack just as it comes back up, so you can fire it off on an energy drain or lustrate if appropriate.
How you "get" to play SCH in a raid setting is very much dependant on your WHM's ability to be the main healer. If they are a less skilled or experienced WHM in a fight, then you may need to heal quite a bit more for your run. If you are running with a WHM who is super awesome, you have plenty of time in-between healing to pop into cleric stance and apply your DoTs to help push the fight along.
The biggest asset to a SCH is it's Galvanize shield it gets from casting Adloquium. Don't spam it because it is an MP drain, but learn a fight/research it so that you know when a large choreographed hit is coming on the tank to help mitigate the damage. A good example of this is Twintania's Death Sentance ability. It happens at a set interval between each cast (idr when) and has a cast time notifying you when it will strike. Basically apply the same reasoning with Succor to party healing, use it before a large hit (like Aetherial Profusion) occurs to help minimize the damage taken.
Also remember that it is a pet healing class, Selene is the support fairy who gives a useful Spellspeed up buff and a less useful Skillspeed up buff. She can still perform her functions if on Sic, but it's better to just micro manage her on Obey. For a lot of farm content and non-heal intensive fights, Selene is the best choice.
Eos is the healing pet, she has 3 self explanitory buffs that you can use to help AoE heals. Generally use her if there's a lot of damage going out to the party in shorter intervals.