Instructions
Choose either the squire or the chemist class for your characters. Each subsequent class is unlocked by leveling up these basic jobs.
Fight battles with the characters for whom you want to unlock other jobs. Your characters will receive experience points as you win various confrontations.
Continue to fight and gain experience until your squires and/or chemists reach level two.
Open the main menu on the world map and choose "Formation." Pick characters who have reached level two in their job class and open the character menu. Choose the "Change Job" feature. You will now be able to change squires into knights or archers and your chemists into priests (white mages) or wizards (black mages).
Repeat this process for each new job class. Some jobs, like ninja, dancer and mime, require you to have multiple jobs at prerequisite levels. The best way to unlock all the jobs in "Final Fantasy Tactics" is to level up each new job as you get it.