I've tried doing things like that, such as having a friend poly a mob,or buff/heal me while i tried to powerlevel, it didnt really work out as being better than just going solo. youd be better off having your friend farm and give you money so you can buy gear. the problem is it takes too long to kill the mob, and by the time your done you could have killed three mobs your level in the same time/with the same mana, so it really isnt worth it.
Best bet for trying to level really quickly is to solo grind. I wouldnt recommend group grinding, you find out quickly grouping isnt worth it. I would recommend leveling on mobs that are 1-2 levels below you, as a mage that was my best bet. On my rogue, i would commonly grind on greens that were 3-4 levels below me, the reason being that my hit % and my enemies miss % were so high i barely expended any hp on each mob, and my energy came back within seconds, so i could basically be fighting continuously