How Can I Apply DoT's Most Effectively?

[JoeDono]

I can answer some of the questions related to BLM.

If you have more than 3 enemies, you'll do more total damage per skill if you focus on AOE attacks and don't bother with DoTs. The only thing DoTing more enemies up gets you is more chances for Thundercloud, which is good damage, but completely up to RNG.

When making the decision on whether to AOE or focus on single targets, it depends on how hard you want your healer to work and for how long as well as your party composition. If all the enemies are alive until the end, then the healer has to work for the entire fight and cannot DPS. If you're paired with another BLM or a BRD with strong AOE, go buck wild and AOE everything. If you're paired with a DRG or a MNK, who can AOE but it's lacking, then you can focus down one monster at a time. It also depends on your tank. If your tank cannot hold threat on more than one monster (maybe he's undergeared), then hold back a little.

Finally, regarding Thunder 1/2/3, the only difference is mana cost, casting time, and duration. Initial potency and individual DoT tick potency is equal. In order to decide, you need to look at how long you spend in Astral Fire and Umbral Ice. How long does it take for you to get to full MP during Umbral Ice? For me, casting Thunder 1 isn't enough time for me to get to full MP, but Thunder 3 keeps me casting for an extra MP regen tick or two. Therefore, I can cast Thunder 2 and be timed perfectly to resume my Fire rotation as soon as my MP fills up. Also, how long am I in Astral Fire? For me again, Thunder 1 falls off before I've run out of MP, so I've lost damage, but Thunder 3 ends up having 7-9 seconds left when I run out, forcing me to clip the duration and lose damage again. Therefore, Thunder 2 is still the best option for me. There are three exceptions. Occasionally, after I switch to Umbral Ice, I only have enough MP for Thunder 1. No matter what, it'll be a DPS loss to wait for an MP regen tick (ABC = Always Be Casting), so cast Thunder 1 just to get the DoT going even though it's going to fall off before I re-apply it. Now that I think about it, it'd be much better to use Convert before switching to Umbral Ice, casting a few more Fire 1, and having enough for Thunder 2 after the switch to Umbral Ice. The second case is the pull, I usually start with Thunder 3 and try to time it so it lands just as the tank pulls. The last case is Thundercloud. Always use Thunder 3 when Thundercloud comes up.