Effective monk leveling build

As far as I know, the fastest way to level up is by doing quests.

Have you got to Gunnar's Hold in Eye of the North?

You can find Kilroy Stonekin there and repeat the quest "Kilroy Stonekin's Punch-Out Extravaganza!". You can run straight to the end boss if you don't like fighting, otherwise the foes give good experience and items as well. The quest reward experience can also level up heroes.

And/or use scrolls for up xp more fast.