When you get to The Upper Abyss you will want to fly south past the Ruins of Roah to the Garden of the Dead. For a better idea of where you are going take a look at my map below.
Over here you will find level 31 Ghosts, Drakes and Guardstones. These mobs will take you up to level 31. Once you reach level 31 you can go to the islands that are further south of here and kill the level 32 mobs.
The further south you go on these floating islands the higher level mobs you will find. The highest level mobs you will find on these islands are level 33 and they are at the very southern end. The whole "Garden of the Dead" and "Shattered Temple" area is quite safe for you to level up in.
The only reason the Asmodians ever come over here is for their Material 100-slot cube quest. Or because the Elyos are bothering them over at their locations. When you reach level 34 you will want to make a hella long journey across The Abyss over to the Undead Island.