Write a brief statement of the poem's purpose before you begin recounting the story - say, to detail your dog Champ's heroic crusade against backyard birds - followed by an invocation of the Muse.
Give a short, general outline of the action of the poem in the statement of the poem's purpose.
Invoke the Muse next by first praising her, then by asking her to aid you in the writing of your poem. The Muse of epic poetry was Calliope, but you can also invoke Thalia (Muse of comedy) or Melpomene (Muse of tragedy).
Choose a particularly heroic event in the hero's life at which to start. This will be the main action of your poem.
Begin the narrative by employing "in medias res" or "framework" narrative. Literally meaning "into the midst of things," this is a poetic convention in which the narrative begins in the middle of the main action and earlier events are retold through flashbacks. The past actions thus form a framework centering around the main action.
Confront your hero with dangerous monsters and other incredible adventures. Include vivid and explicit descriptions of warfare (particularly weapons and combat).
Use the supernatural to get your protagonist out of tough situations. If your hero or heroine is in a no-win situation, simply send in a god or goddess to help out at the last moment.