BLM Help

[Malevicton]

When you use transpose to switch from fire to ice your mana will usually regen before the cooldown is back up. If the timing ends up being strange (maybe you had to dodge some aoe or something) then you may as well use it to buff the start of your fire rotation... but the shorter answer is that you only need to use it when switching from fire to ice.
Once you get more practice in on the rotations, and get a feel for the timing, it'll start making sense.
Tbh though, I wouldn't get too invested in these rotations. You get fire3 at 34 and blizz3 at 38 and having both of those will make a pretty big impact on how you play.

Edit: As an unrelated aside, you'll eventually want to get raging strikes as a cross-class ability from archer. One of the best offensive cooldowns in the game.

[Ferth]

...As an unrelated aside, you'll eventually want to get raging strikes as a cross-class ability from archer. One of the best offensive cooldowns in the game.

Since unlocking blm requires archer at 15 it's a foregone conclusion that you will have raging strikes. The really important ability from archer is at level 34, quelling strikes.