Leveling from 1 to 60 is quite easy nowadays, there are many XP bonuses and you can get to Outlands in quite a short time. However, when you reach the Outland zones, once you pass level 60, and furthermore, when you pass to Northrend, you might want to enhance you advancement by completing one or two dungeons.
To gain a high amount of XP in instances, it’s best to aim for the ones with a heavy load of trash mobs. Those are the instances from 60 to 80 that I’m going to point out here.
So, here’s my dungeon leveling path for Outland and Northrend:
58-60 – Hellfire Ramparts.
60-64 – The Underbog. Excellent place to rise your Herbalism. Also, pick up all the Sanguine Hibiscus and sell it in stacks of 5.
64-67 – Mana-Tombs. If you’re an enchanter, you’ll get a chance to get the Formula: Enchant Boots – Fortitude.
67-70 – Shadow Labyrinth and/or The Botanica.
70-73 – The Nexus.
73-76 – Drak’Tharon Keep.
76-79 – Halls of Stone.
79-80 – Caverns of Time: The Culling of Stratholme.
If you join groups for these instances when your character is within the level range mentioned, your effectiveness in a group will be optimal and the XP/time rate, maximized.