I was the loser that had everyone master everything but I think the best thing to do at the begining is make sure that you spread out the type of jobs you're learning among your party members - for example, don't have four mages at once to start, you'll probably get killed. I generally do two and two - two members will concentrate on physical attack jobs, while the other two will work on magically powerful jobs, then switch. It balences out your party well, so that soon you have characters which are strong as both fighters and mages - hence the true greatness of the FF5 job system.