I've heard people say that you should have watched 800 dance performances before you begin as a critic. I'd only seen about 250 when I began. I've heard other people say you should have been watching dance for twenty years. I'd been going frequently for less than two. A friend of mine said the other night that "There's no such thing as a good young critic." Her point was that a critic who's only seen three Ophelias doesn't know enough, whereas someone who's seen 20 does. Well, even now that I've seen more than twenty Ophelias, I still don't agree. I would rather read a fresh critic coming new to the art form with all his/her wits than an old-fart critic who's tedious to read.
Those ideas about experience propose that a critic must be an expert. I, however, believe that criticism begins not in knowledge but in ignorance. You can't prepare for a new ballet, a new dancer, a new play, a new work of music, a new trend. Expertise won't help you with the new; but an open mind will. And actually you can't prepare for the qualities that will make your 300th "Swan Lake" different from the previous 299.
Take that, John Lahr!
(h/t Thomas Cott)