Well This is my leveling guide in iRO, This is best used with a physical attack character. It has gotten me to 95 in a little over 3 months.(Taking my time not power leveling 10hrs a day)
Novice 1/1 - 13/10- Training grounds
1st Class 13/1 - 35/2x- Culverts (Mobs) or Payon Cave (I suggest a blast clip for either.)
1st Class 35/2x - 2nd class- Metalings (einbroch)
2nd Class 51-55/1 - 65/3x- Zenorcs
2nd Class 65/3x - 75/4x- Lou Yang or Gonryun dungeon 01.
2nd Class 75/4x - 85/50- Gonryun dungeon 01. ( Its not about the amount of exp from the monster, Its about the amount of exp you get the quickest.
2nd Class 85/50 - 99/50- Turtle dungeon or Bib05.
I'm not saying this is the perfect way or its the best. Its just a fast way to level that worked great for me and 2 of my friends.