The epic is centered on a hero who determines or is majorly involved in shaping the destiny of a group of people or a community. Epic conventions are basically characteristics of such narratives and they include:

• A hero or an ideal individual within the community
• The narrative covers a wide geographical scope and takes the reader from one region to another
• The narrative will concentrate on actions by the hero that are beneficial to the community
• The narrative may also blend in some supernatural forces
• The protagonist may be introduced at a lower level in order to be elevated during the course of the story

Paradise Lost is predominantly centered on the supernatural and tells the story of Adam and Eve and how they “lost paradise”. There are arguments about who the hero in the story is with some supporting Satan while others siding with Adam. In my opinion Adam is the hero because he fulfils most of the epic conventions. Adam is first portrayed as weak when tempted by Satan through Eve. He however emerges as the hero of mankind when he prevents Eve from committing suicide. In the story he is in constant communication with angels such as Raphael and Michael. He is also portrayed as a wise man who understands Satan’s eventual defeat by the Son who will be born as a man. The epic also takes the reader to heaven, hell, paradise and earth which are geographically distant realms.

Epic conventions are literary devices used to establish the genre of epic poetry or prose. Epic conventions were first created by the poet Homer. In "Paradise Lost," Milton uses epic conventions to help the reader understand the nature and purpose of his work. In the beginning of the poem, Milton calls upon the muses. This is an important conventional technique that gives literary credibility to the work. "Paradise Lost" describes a story familiar to the readers, using characters the readers already know. It explores the relationship between divine characters and human characters. It emphasizes fate over free will, as the characters are powerless to escape their destinies.  

As a Puritan, how does Milton employ classical epic convention in his invocation in Paradise Lost?

It is well worth considering how Milton in his invocation in Book 1 of this epic classic both upholds the conventions of invocations in other epics but also subverts them and brings his own Puritan world view into what he writes about. This invocation of course bears many similarities to the invocations in other epic classics such as Homer's The Iliad and The Odyssey. Such works appeal to a muse to help the poet achieve their purpose and also use elevated and grandiose language in their invocation. In addition, the invocation indicates that this classic starts in media res, or in the middle of things, as other epics do as well.

What is different is that Milton brings to his writing a Christian sensibility that springs directly from his Puritan background. Whereas other epics are pagan in nature, focusing on the relations between a pantheon of Gods who war against each other and use humans as their toys to further their own purposes, Milton states in his invocation that his epic classic is written to do nothing less than to "justify the ways of God to man." The invocation is full of Biblical imagery and allusions that support this purpose:

Of Mans First Disobedience, and the Fruit

Of that Forbidden Tree, whose mortal tast

Brought Death into the World, and all our woe,

With loss of Eden, till one greater Man

Restore us, and regain the blissful Seat,

Sing Heav'nly Muse, that on the secret top

Of Oreb, or of Sinai, didst inspire

That Shepherd, who first taught the chosen Seed,

In the Beginning how the Heav'ns and Earth

Rose out of Chaos:

You can count the references to important Biblical characters and themes, and in order to answer your question you would do well to compare this invocation with the invocations of other epic poems in order to explore further the distinctly Puritan nature of this opening.