Here's an overview of all of the DS Classes.

Other than that, use Phoenix Downs sparingly because you can't buy them in this game. The jobs also work a bit differently than other Job Class FFs in that you're kind of meant to drop classes for their upgraded version but the DS version tries to make the classes a bit more balanced so you can use any party build you want.

There is also a Job Level Proficiency stat where leveling up grants you bonuses for skills and stats. Once it's maxed out, there is a special blacksmith in the game who will forge a unique item for that particular job class.