If there's nothing specified for the boss assume it's normal heals
Arachnid Quarter
Anub'Rekhan - If you're healing the MT, keep a 30+ yard distance from Anub, he casts locust swarms which silences everyone within 30 yards for a few seconds.
Grand Widow Faerlina - Keep poison totem down, extra heals on the tank when Faerlina enrages.
Maexxna - Heal people as they get webbed. Extra heals on MT after 30%
Plague Quarter
Noth - Decurse as necessary
Heigan - Stay 20+ yards away from Heigan in phase 1, Use disease totem, get in the right zones in phase 2.
Loatheb - Heal assigned players in the 3 second window allowed.
Military Quarter
Razuvious - Just heal assigned target
Gothik - Heal as necessary
Four Horsemen
-10 man. The healer in the north corner heals himself and that tank. The healer in East heals himself and everyone in that corner. South/West heals himself and the ranged assigned to the other spot.
-25 man. The healer in north heals himself and that tank. The healers in East heal themself and everyone in that corner. The healers in South/West heal themself and their assigned tank.
Construct Quarter
Patchwerk - Big heals on your assigned tank the entire time.
Grobbulus - Get to a safe zone when injected, heal assigned target(s)
Gluth - Heal assigned target. If you're not tank healing be ready to heal fast and quickly after decimate.
Thaddius - Very easy to fight
Frostwrym Lair
Sapphiron - Heal though high damage, unavoidable AoE in phase 1, get to the outside walls in phase 2.
Kel'Thuzad - Minor heals in phase 1. Save instant cast cooldowns for icet ombed people in phases 2 and 3.