use mana shield, THEN this spell, get on your mount and go grab 12-20 mobs (whatever's in the area). if you do mana shield after this, you're draining mana when you don't have to, using this shield alone may be taking a chance of becoming dazed once this spell cuts off, but w/e.

grab a bunch of mobs, wait til they're close together, nova and run back (or blink if you really want to, i've never had to) to blizzard range's max, pop 2 blizz's off and nova again if your mana's low (by opinion), use a gem while you're running, jump, flip backwards and how you wanna finish the mobs off, you have the oppurtunity to use fs (if you're a shatter built mage, fs works lovely with ignite right here), ae, coc (first to laugh dies), or even a bomb if you're eng (not sure why mages would be eng though) (other than frost grenades, or trinkets that is)

I did not get the Ice Shield at lvl 40. Is it part of a quest or something?

at 60 it absorbs 835 dmg orsmthing , my mana shield absorbs more , in pvp it totaly sucks, 1 hit and its gone ... only good in 5 man instances, since they only hit 100-200 there

Aye! If you are a frost specced mage is this much better than PoM.