Alright this is nothing new, and may be common sense for many people, anyways please tell me if there is any previous post that is similar.
best done by dagger rogues and mages w/ POM
Simple. Go to the inn of some faction-independent towns e.g. Gadgetzan
go to the inn. find a player of opposite faction. for rogue, just go behind your prey and stealth, and press macro
/camp
/cast Ambush
and for mages just POM and then /camp /cast pyroblast, can even kill people near the entrance of the inn. you should see them lying dead mysteriously after logging back
cheers