Mirabile dictu… just as we need to have read widely before attempting to write, so too for the incomparable Shakespeare. His preference : mostly the classics and other canonical works by early  English authors (e.g., Edmund Spencer and Sir Philip Sidney).  The English Philosopher Thomas Spencer Baynes of the University of St. Andrews takes a shot at the subject of Shakespeare’s reading preferences.

http://qz.com/668693/400-years-after-his-death-here-are-the-books-that-likely-influenced-shakespeare/