In both Greek and Latin, the most common epic meter was dactylic hexameter. That's a difficult meter to pull off in English, though; English epics aren't associated with any one meter, though most of them beginning with Spenser are in pentameter. Famous English epics include the Old English poem Beowulf (written in alliterative meter); in the Renaissance, Spenser's Faerie Queene (with its complicated Spenserian stanza) and Milton's Paradise Lost (in blank verse). In the late seventeenth and early eighteenth centuries, heroic couplets were considered the best form for epics; Dryden's translation of Virgil and Pope's translation of Homer use heroic couplets.
The history of the epic is worth studying in some detail. The Iliad, Odyssey, and Aeneid are the most famous epics of antiquity, but not the only ones; Statius' Thebaid, for instance, is worth reading. In the Middle Ages, the dominant long narrative form is the romance, which is epic's kissin' cousin. Exactly what to call Beowulf is unclear, but Dante's Divine Comedy is probably best described as an epic
As you get into the Renaissance, the familiar pattern of the classical epic becomes more visible: Ariosto's Orlando Furioso (1516) mixes romance with epic, but Tasso's Gerusalemme Liberata (1575) is clearly modeled on the epics of Homer and Virgil. Camoens's Lusiads are the great Portuguese epic. The first great English epic of the Renaissance is Spenser's Faerie Queene (1590-96), followed by Milton's Paradise Lost (1667-74).
But then the form seems to disappear, or at least to trasform itself radically. In the late seventeenth century, most writers were convinced that epic was the highest form and yet, according to most conventional histories of English literature, no one succeeded in writing a great one. There are good translations of the classical epics by Dryden and Pope; there are also brilliant mock epics. Henry Fielding incorporates many epic features into his novels (he calls Joseph Andrews a "comic epic-poem in prose"). In the early nineteenth century, Wordsworth tries to write a kind of epic, The Prelude, but it's a very loose fit with the traditional definitions.
Sometimes it's unclear whether a particular work is best called an epic. Gilgamesh, for instance, works on a scale similar to most epics, but it's not directly related to the Homeric tradition, and lacks many of the characteristics of the Western epic. Ditto the Indian Ramayana and Mahabharata. In the West, many works of the Middle Ages and Renaissance blend qualities of the epic with the romance there were plenty of squabbles between the supporters of Tasso and Ariosto in sixteenth-century Italy over how much romance can be admitted into epic. And after the decline of the traditional epic in the seventeenth century, many works borrow many epic characteristics, though again, it's unclear whether they should really be called epics. Melville's Moby-Dick, Tolstoy's War and Peace, Joyce's Ulysses, Derek Walcott's Omeros all have epic characteristics, but it's unclear whether they're properly epics themselves.
Whatever you do, though, don't use the term epic loosely for anything large in scope. Although networks will try to convince you every miniseries and telemovie is "epic," don't believe 'em or, at least, don't use that sort of advertising cant in an English class.
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.