THM/BLM basics:
Are you ....
- ...pressing the button for your next spell before the current spell finishes? This will queue the next spell to begin casting immediately, so that there are no pauses.
- ...casting Fire until out of MP? Even though Fire and Blizzard have the same tooltip potency, Fire spells get a bonus while under the effect of Astral Fire. Later, at three stacks, Fire spells will do almost double damage (180%).
- ...Transposing to Umbral Ice when out of MP, and then casting Blizzard until MP is full and Transpose is available again? This will give your MP time to refresh. Once it's full, you can Transpose back into Astral Fire and start spamming Fire spells again.