The biggest mistake I see undergeared people doing is playing rambo. Like a undergeared dps trying to 1v1 a geared healer, then qq'ing because he couldnt dent him.
If youre undergeared, stay with a pack, do alot of cc, peels, and things that contribute to a win, but not necessarily trying to top the charts for kbs and or damage.
Queueing in groups helps too.