The best way is to continue to harvest and make items for your profession. Or you could do the storylines for each area, which are very redundant. I don’t recommend dungeon leveling because of how boring it gets.
From my experiencing leveling 20+ characters over the years, the easiest/quickest methodis tokeep queuing for random dungeons non-stop, and complete world quests with high-density/small area while you wait for your queue to pop.
To speed up the process, apply any sort of experience-boosting buff you can get your hands on, such as the Darkmoon Faire carousel buff, or one of the XP-boosting items from various expansions.
Also, make sure you step into an inn or city before you log out each time, allowing the rested XP to build up while you are offline.