One of the places that I liked to lvl my lvl 1 pets was with the battle trainer in Deadwind pass because the elemental always seemed to open with thorns which was good for me. So I brought in my lvl 1 pet and instead of thorns he comes over and poisons me. First time I had seen him use that ability and it was against my lvl 1 pet and my pet dies.
Now I still use that battle tamer, but I make sure that one of my frogs has Cleansing Rain
ready to use and then I don't have to worry about the poison.
I have learned to never try to lvl a pet against a spider. Stupid web. I will still forget against turtles sometimes and their Grasp
ability gives me a bad day.
Dragonbone hatchlings in Dragonblight often start with cyclone which doesn't kill my lvl 1 pet on the first go-round, but sometimes will kill them when they're in the back row.
They're not very prevalent in Icecrown, but whenever I find a cockroach I use him to lvl up a lvl 1 pet. Their attacks are usually pretty weak and wont kill my pet and they mostly just start with Apocalypse
which does no damage whatsoever. Then I use my flayer youngling for choping up their team and 1.5 minutes later I have a new lvl 5 pet.