Your rotation doesn't become fluid until 40(?). Its been a long time since I was blm below 50, so I don't remember when certain traits become available. But basically when Astral Fire III and Umbral Ice III overwrite eachother, you become the BLM that the game intended you to be. You'll get a speed boost when casting Bliz III from AFIII and vice versa for Fire III from UI3. At that point, you only use transpose when you are out of mana completely OR, to get into astral fire and use a firestarter proc.