At NMI, we try to treat our members as professionals. Some would say that the difference between a professional and an amateur is a paycheck. But here are some more useful ways of thinking about the differences:
Professionals arrive for rehearsals a few minutes ahead of time; amateurs allow themselves to be late.
Professionals show up prepared; amateurs show up unprepared.
Professionals take responsibility for their work ethic and creative process; amateurs often look for someone to blame.
Professionals seek out constructive feedback; amateurs get defensive and think of feedback as criticism and judgment.
(etc. You get the idea.)