I'm a critic. That means you are a writer. So, yes, you have to make yourself an authority on whatever subject it's going to be. Music, movies, literature, whatever it's going to be, but what you really want to do is learn your trade by reading other writers. I think you have to read veraciously, especially people who have done what you have done to see how it's been done in the past; what works, what doesn't work.