It depends on what kind of a job you have... But one thing is for sure: school should be on the first place. You wouldn't wanna have a job during school, and don't finish school, and then remain at the same job level, right?? Everyone wants to evolve...

Perhaps the best advice is to organize your time schedule very well, always know ahead perfectly all the spare hours you will have available for homework, leisure time, to study for exams, to socialise, and so on.