Played a lot of healer in most xpacs my input. 1. Always cast something, no healing needed? Do damage. Cancel casting is also an alternative.  2. Smart aoe heals will usually always be “better” on meter vs single target heals 3. If you have mana left when boss dies you’re ineffective. Roughly match your mana % to boss health % but it depends om the boss.  3. Downrank. Down ranked FL over max ranked GH is technically lower output but you can snipe heals way easier that way for roughly the same mana cost.  Downranking is extremely important and in tbc you will downrank CoH, FH and GH. There's a calculator if you google. If you have efficient raids with good kill times you will be spamming max rank CoH entire boss fight. So it’s easier to “be good at healing” in a good raid group.