At lv 52, you can apply a regen while applying your DoTs to the enemies the tank has tagged. This will lower the HP of the enemies in the long run as he goes to the next pull and reduce the amount of healing in the long run since enemies die faster once the tank stops pulling. Give the tank a heal if required on the move, but generally the regen would be enough if the tank has decent gear and is competent + your gear is decent since the tank should be able to outrun most of the enemies. Pop a sprint if the tank is sprinting too. Notable uses of instant cast healing are Afflatus Solace (700 upfront heal on the GCD), Tetragammaton (Lv 60 700 potency heal), Benediction (Full heal, used when tank is getting low), and Assize (400 pot heal + 400 pot damage, used on cd unless holding it for a couple of seconds can save a GCD heal).

Once the tank finishes the pulls and proceeds to AoE everything (you can generally tell by experience or the tank pulls to a wall), proceed to either swiftcast holy or manually cast holy. Holy is effectively an AoE stun with diminishing returns to its stun. Not only does it prevent most enemies from doing damage, it lets the tank heal up with their passive regen + applied regen. This will slow the amount of incoming damage to the team + helps DPS. For optimizing holy usage, you should only delaying using holy if you know you can save casting healing GCDs since holy's stun can interrupt a trash add's skill, but otherwise you should be using holy as much as possible since it also helps reduce the enemies' HP - and thereby helping you kill them faster + heal less as dead enemies can no longer do damage.