This is how i do this, im sure there are other ways that work just as good.
Things you need are.
1 lvl 80 necro(can only be one 80 in the group/raid)
group or a raid
A little time
A good spot to power lvl(DMC/East Ruins)
After you got you group/raid together head to your favorite plvln spot. Have the necro run get the biggest mob he can handle.
So as the necro has got agro from the WHOLE mob he/she pulled, kick necro from group, and BAM!!! everyone that is left in the group/raid will get 2k xp a kill. Went from 50-60 in a few hours.
Enjoy