THM Rotation Help Plz....

[Delta041]

The reason why you want to use transpose instead of just switching from Fire 1 to Bliz 1 is that you will drop your stack and loose out on bonus damage/MP regen until the next stack begins.

It's more efficient to use Fire1 until you can't cast anymore, transpose, and start Bliz 1 while building up MP faster since you'll be in Umbral before even casting Bliz 1. Once your MP is maxed you transpose from Umbral to Astral so your first Fire1 has bonus damage. As a THM/BLM you want to maximize the time spent in Astral and minimize your time in Umbral

Once you get Fire and Bliz 3, they will give you maxed out Astral/Umbral stacks when cast, letting you finally drop your transpose.

[Asheilin]

The reason why you want to use transpose instead of just switching from Fire 1 to Bliz 1 is that you will drop your stack and loose out on bonus damage/MP regen until the next stack begins.

It's more efficient to use Fire1 until you can't cast anymore, transpose, and start Bliz 1 while building up MP faster since you'll be in Umbral before even casting Bliz 1. Once your MP is maxed you transpose from Umbral to Astral so your first Fire1 has bonus damage. As a THM/BLM you want to maximize the time spent in Astral and minimize your time in Umbral

Once you get Fire and Bliz 3, they will give you maxed out Astral/Umbral stacks when cast, letting you finally drop your transpose.

^^ is pretty much it. My fiancee has been trying to teach me BLM (mine's at 30, he just hit 50) so this may not be 100% accurate but:
Thunder/Thunder II first, keep it up multi-doting another mob is ok; more then two you're wasting damage. Always reapply when it procs.
Fire I for single target rotation, until you get Fire III. By that time you should have a good feel of which one you should be using.
Blizzard I for single target rotation, until you get Blizzard III.
Transpose whenever you're out of mana then start Blizzard I; Transpose again when full to switch back to fire. I like to transpose when battle ends as well, this means you're rarely low mana between pulls (unless they're pulling quick, then probably not needed)
Single Target Rotations is for 1-2 targets, usually.
For everything before 50, you'll use Fire II during Astral and Blizzard I/III during Umbral as blizzard II is melee range and is rarely safe for your health.
At 50, you get Flare. This is your true AOE spell.

http://forum.square-enix.com/ffxiv/threads/112288-The-Black-Mage-Rotations was the defacto BLM forum, idk if it still is. Hope some of this helped/clarified things.