aoe spots:
20ish: redridge mountains; small groups of gnolls and orcs, at this level you don't have ice barrier, so it's a little hard to pull with just mana shield.
30ish: duskwood; the worgens are packed pretty close together, but still don't have ice barrier.
40ish: there is an island off of the northeastern coast of theramore isle with lots of murlocs and absolutely no horde because it's so remoted, no one ever goes there, and now you have ice barrier and shatter barrier for the aoe pull.
50ish: WPL, the big graveyard near the WPL flightpath with all the zombies and skeletons, much easier at this point with your spell dmg gear and more talents.
outland: temple of telhamat: in front of the temple there are lots of birds, they are very close to each other and fairly easy to pull.
haven't got to northrend yet but i remember seeing someone wrote down some spots, i just don't remember the names.
basically once you have ice barrier and shattered barrier, put it up, mount, and run around the mobs to get aggro on lots of them, but try not to get hit too many times. once you round up all of them, try run around in circle a bit to group them together, then get hit on purpose to shatter your ice barrier. blink after they are all frozen in place, then blizzard them down. depending on their remaining health, you can either cast a 2nd blizzard right in front of you or just use arcane explosion. when i got to western plaguelands i had 110 ish spell damage, it was enough for me to just use 1 blizzard to kill half of them then AE the rest of them down when they got close, 2nd blizzard became an overkill.
before you have the ice barrier combo, you have to use mana shield and frost nova; but remember, even after you have ice barrier, you can still use mana shield and frost nova to pull the extra mobs and nova in case of emergency (resist or missed the aoe of shatter barrier); even pull out an water elemental for the extra frost nova.