Was reading some stuff about freeze some pages ago -

The problem with Freeze is that bind will vanish once you attack the mob who is bound by it. Sleep + Deep sleep is lot more useful in a crowd. Making them unable to attack the tank and giving you extra 30 seconds, a heaven for the tank and the healer. The duration gets shortened after every time you use it though so I would myself use Sleep until they fully resist and then freeze to bind them. However I only see Freeze' use in a crowd, or when you want to space yourself, gain mana cuz u fked up. I'm sure there are other uses as well. But I go with Freeze in a defensive option. It saved my life already some times. But it's really REALLY situational.

As for flare... I'd guess it's use is to do massive AoE damage. I wouldn't use it for a single mob. Or for the final hit to make things flashy :V

My usual (Boss) rotation is -

Thunder III - Fire III - Fire nuke till round 100 mp left - Blizzard III - Thunder III - repeat.
When being in Umbral Ice III my Mana actually regenerates once after I have used Fire III making me have full mana + Astral Fire III. On bosses I usually use Raging strikes after I've gained Astral Fire III, convert for more fire, and swiftcast for even more fire

On usual mobs I leave the Thunder III out unless they have a huge amount of health.