Hrm - this may have been changed in more recent patches but to easily get a few levels on a new character you used be able to:

Return silithus dust to the converter - requires a high level chaperone to keep all the bugs off you.
'Tag' three ridiculously high level mobs for your char (i.e. a level 5 tagging three lvl 15's). Have an un-grouped paladin with retribution aura turned on taunt the mobs off you but now no 'active' damage. Used to be that since the damage was reactive rather then active that the exp penalty wasn't applied.
Avoid un-necessary collection quests and cycle from zone to zone. By this I mean do ALL of the quests in the starter area until you get to level 10 - this should exhaust most of the quests in that start region so go to the end of another races starting area - once again avoid collections quest unless they're part of a chain that's worthwhile. Personal experience of this had me levelling about 15-20% faster - then again I had a warlock ready each time to summon the low level char to the next 'quest rich' area.