Depending on the program, it'd be wise to become familiar with:
Walter Benjamin
The Work of Art in the Age of Mechanical Reproduction
Theodor Adorno
Michel Foucault
Susan Sontag
Maybe Slavoj Zizek
this book on Robert Irwin
http://lawrencewesch...-thing-one-sees
You can check out books by Jerry Saltz, Roberta Smith, Dave Hickey. Some folks still want you to read Clement Greenberg...,
There are a lot of people writing about new genres, social media, visual culture. It can get overwhelming. If you want a head start, you might peek at your fav University's reading list.