In his article on The Power of the Marginal, Paul Graham suggests (among other things) a way of picking courses at college.
One way to tell whether a field has consistent standards is the overlap between the leading practitioners and the people who teach the subject in universities. At one end of the scale you have fields like math and physics, where nearly all the teachers are among the best practitioners. In the middle are medicine, law, history, architecture, and computer science, where many are. At the bottom are business, literature, and the visual arts, where there’s almost no overlap between the teachers and the leading practitioners. It’s this end that gives rise to phrases like “those who can’t do, teach.”
Incidentally, this scale might be helpful in deciding what to study in college. When I was in college the rule seemed to be that you should study whatever you were most interested in. But in retrospect you’re probably better off studying something moderately interesting with someone who’s good at it than something very interesting with someone who isn’t. You often hear people say that you shouldn’t major in business in college, but this is actually an instance of a more general rule: don’t learn things from teachers who are bad at them.