Step 1. Get a bunch of cheap forcium items or as close to 1k defense as you can.
Step 2. Get Auto HP heal Items (Not potions).
Step 3. Get as much Pet Exp % bonus as you can.
Step 4. Go to Pontus Ferrum at the center ring right next to those starting portals and grind on 1 Brachium. (Yes not Cornus, because hunters of pet grinders will kill you either mob you're attacking, so why cost yourself extra work?)

Over the past week I have leveled a Nipperlug to Lv 6 with 40% in 7 days. (I did alot of afk though)