Goal oriented and very focused. Lot of time to spare doesnt hurt I have noticed going solo helps a lot too, I levelled my second 60 solo from 44-60 in probably the same time I levelled 52 or 53-60 when my wife and I levelled "where" and "laraptor". I prefer the group aspect and being with friends though so I havent been levelling very fast at all this time around hehe. That and we havent had near as much freetime with everything else going on IRL.
on avrage if you are questing and grinding only rather then running instances or helping lowbies out you can grow about a level in one day easy, you just have to make an effort.