Fastest way to grind job levels in FFIII
Why would you need to farm your job levels? Job level has a direct impact on your characters’ damage dealt. It is worth grinding at least a bit when you switch a character to a new job in order to maximize their damage output.
This can also be handy for getting the job level related achievements early, but those will all eventually pop during a normal playthrough, anyway.
Where and how: the process
This can be done anytime after completing the opening dungeon. I recommend this location because Goblin battles go quickly and you won’t need to stop to heal or cure status ailments during the process.
Wander the grasslands around the starting town of Ur
When you get into a battle, attack with your first party member and have the rest defend until there is only one Goblin left, then switch your attacker to defend
Since we need 5 rounds of battle and Goblins are a one-hit kill you need to defend enough rounds so the last kill is round 5. For example: if there are 4 Goblins then kill 3, defend 1 round, then kill the last one. If there are 2 Goblins then kill 1, defend 3 rounds, then kill the last one.
If you do it right, you should gain 1 job level for everybody for every battle
If you get a good rhythm down of engaging/disengaging the auto-battle then you can get from 1 to 99 on all four characters in less than 30 minutes (faster if you hack the auto-battle speed)