knowledge of optimal quest pathing and the locations of some the treasures. if you don't pick up treasures you are going to HAVE to do every quest in each zone (exception might be Gorgon due to all the bonus objectives), if your leveling in a group drop guild banners when fighting large packs of mobs and they work on treasures also.
my first play through just from 90-100 took just over 14 hours and i didn't read quest text, my 2nd time i shaved off 2 hours.