This trick even works better for classes such as a mage and a warlock
There are two ways to get very fast exp, for most classes this trick can only be done once you reach lv 10+
One of them is healing ( any healer )
One of them is tanking ( a warlock )
Example:
I have a lv 15 warlock, i have 2 instant cast spells: corruption(talent) and curse of agony.
I take all the quests in the zone.
I have a friend who can heal me, if i party with him i wont get much exp, so instead you use commen sense and dont party.
I pull as much monsters as i can, i use coa and corr on very single mob, i use lifetap to get my mana back.
All the mobs will die and you will get 100% of the exp, your healer will be using low lv heals(becuase wow doesnt allow higher ranked heals to be used on low lv chars) and becuase of that the healer will not pull aggro.
All the quests will be finished very fast aswell.
If i had a friend warlock he could tank the mobs for me, he just casts curse of shadows on the mobs, that will pull aggro, at higher levels 20+ the warlock should cast curse of shadow a few times or i might pull aggro.
The warlock is best in greens with stamina gear to minimize repair costs (me in full epic when i tank for an hour i have 20g repairs,in greens i have 3g)
Warlock with a sacrificed voidwalker (fel stm) will gain additional aggro tanks to the hp regenerating, it is classed as healing (but it doesnt receives extr from bonus healing).
And last but not least my spell do 10% dmg becuase they are debuffed
Warlocks without fel stm will die after a couple of minutes, warlocks with fel stm can lasts for a long long time, but eventually if the mobs dont die you will die
As a mage i would cast arcane explosions or other aoe stuff depending on your spec.
As a shadow priest i would cast dots, it would take a little longer
As any other class (i cant think of any more with aoe capacibilities) i would just attack them one by one and finish the quests real fast without having to wait for health
So if you wanna make an alt, pay your friend a couple of gold for an hour of healing or tanking and if you do it without wasting time you will skyrocket in levels