This is the place to start if you're unfamiliar with Greenblatt (and perhaps even with New Historicism in general, although the book "Practicing New Historicism" is also very good, but the Greenblatt essays can also be found in here). All of the important essays that laid the groundwork for New Historicism are found here plus many that touch on autobiographical and non-literary topics (these are admittedly pretty hit-or-miss though, honestly). Greenblatt and his New Historicism (or, as he refers to his theoretical approach, "Cultural Poetics") is a rich (if flawed) approach that has opened many new doorways of study and work in literature (and even other fields of the humanities). Greenblatt is a great synthesist (he readily admits the many, disparate sources from which he draws inspiration) and in the top ranks of theotricians. But, even without consideration of the theoretical underpinnings of his work, Greenblatt is a great essayist and a good thinker, and a better writer than 99% of academics out there, so that even if you are not won over by his approach, there is still a benefit to attempting his work. Anyone interested in modern theory and/or literary theory should without a doubt look into this work, and even if you aren't, it is still worth investigating.