Black Mage DPS Rotation

Single Target DPS Rotation:I generally start my rotation by casting Fire III > Swiftcast > Thunder III. This allows me to get THREE stacks of Astral Fire right off, and also get my DoT ticking immediately.

Single Target DPS Rotation Example: Fire III > Swiftcast Thunder III > Fire > Fire > Fire > Fire III(firestarter proc) > Fire > Fire.

Mana Regeneration Rotation Example: Three stacks of Astral Fire > Blizzard III > Thunder II or if you have Thundercloud proc Thunder III > Fire III.
Entire rotation example: Fire III > Swiftcast Thunder III > Fire > Fire > Fire > Fire > Fire > Blizzard III > Thunder II > Fire III , etc. etc.

Area of effect DPS Rotation: Fire III > Fire II > Fire II > Fire II> Flare > Transpose > Blizzard II > Blizzard II > Fire III > Flare > etc. etc.This will be the only time you use transpose as a Black Mage due to Flare using all of your mana.

Other things of note:

Raging Strikes is a great buff granted by level 4 Archer, 20% increase to dps for 20 seconds don't pass that up.

Convert is good for getting extra casts in or if you run out of mana in a high mobile fight because of stacks dropping.

Thundercloud procs should only be generally used in mana regeneration phase, as it takes two global cooldowns to recover all of your mana.