The best way to level ( For me and others that i have noticed )
Though i will say this DO QUESTS you get more exp for doing them then grinding but i will leave the grinding guide up just in case you would rather grind. c:
1-10 : Forest of Tides - Hero Slimes
11-20 : Forest of Mist - Phino's, Greenky's, Smart Phino's, Prock Zones, Little Lizardman, etc.
21-80 : You can go to the Abyss just find the battlefield guard in each town. (Elderine, Uruga, etc)
81-90 : Flaming Mine in Burning Rock - Kill Cursed Knight Gold
91-100 : Temple of Spirit - Black Shadow
101-125 : Arkroute - Technician of the Arkroute (Go to Kahal Snowfields > Arkroute )
126-135 : (Still leveling will update when i reach these levels) c.c