Leveling is most of the early game in Blox Fruits. These habits make it much faster.
Stack every EXP code
Redeem all the active 2x EXP codes. Their durations stack, so redeeming them together gives you a long boost, and the timers only run while you are in the game. Start a session with the codes, not in the middle of one.
Always have a quest
Take the quest for the highest enemy you can beat and kill quest enemies only. Quest EXP is much higher than killing random mobs.
Pick a farming fruit
Area attacks clear groups of quest enemies at once. Flame and Ice are cheap options, Light moves you between islands quickly, and Buddha’s giant form hits whole groups.
Put stats into one build
Spread stats out and you will be weak everywhere. Choose Melee, Sword, Gun or Fruit, and put most points there plus Defense. Stat reset codes let you fix mistakes for free.
Move on at the right levels
The Second Sea opens at 700 and the Third Sea at 1500, and each sea has much better EXP per enemy.