How do I heal?

[Risvertasashi]

I hate to hijack this thread, but I have some relevant questions:

How do I heal in high-level content?
-snip-
but what do I do if the tank's health is going below 50% and he's still pulling?

Second question first: Generally... heal the tank. It's on them for pulling more than they can handle. If you want you can let them die, alternatively. It's a lose-lose scenario.

First question: Same basic principles as earlier in the thread. Learn the fights really well. If you aren't comfortable DPSing for this, then don't; that's OK. DPS (IMO) is for when you know a fight well.

You'll learn when the big hits are coming, what tools are best for what situation. For example, Cure II is very inefficient, but sometimes necessary to get through damage spikes. Cure I spam is more mana efficient, but if you want to DPS, Cure II could potentially let you get back to Cleric faster. HoTs are generally good to have up any time there's incoming damage or will be soon, but try to avoid them just before adds pops. Divine Seal is on a short cooldown; use it often, don't hold onto it "just in case" (like not using it for several minutes). But when you know fights, popping it just before a big damage spike is valid.

Really, look at every single skill you have. Carefully note down its effects. Figure out the best times and situations to use it.

Even Surecast is not useless. (Some will disagree with me on this, but really, I think it's useful on some fights).

Now you might want specific examples. For this, you want to go look at the healing guides to various fights, this one for example. Now to really get the most of it... don't just blindly follow what the guides say. Try to figure out why the guide recommends healing a certain mechanic or piece in a certain way. If the guide doesn't specify... ask yourself: When would be good times to pop my cooldowns? When should I use my mitigation (or avoid it and let the SCH mitigate)? Another example, in that guide above, it's telling you to regen in a way that regen won't be up when the add pops (even though it doesn't say this directly).

Beyond that, have a healer wingman come with you on fights that isn't afraid of telling you where you can improve.