Introduction to Whitman's "Song of Myself" The Poet
The poet, or "myself," in this poem is a poetic persona, not exactly Walt Whitman the man. In many ways, he resembles the poet as described in the "Preface" and in Emerson's "The Poet"--and you might consider just how. He is a transcendentalist, and in this case, it means that every physical detail is microcosmic and has possibilities for greater meanings, so it is important to visualize what sort of person he presents himself as and what happens to him throughout the poem. Pay special attention to the union of body and soul in stanza 5 and what sort of wisdom can come from that transformation. The "self" is much like the "self" of self-reliance as well as a poetic construct--deeply individual yet also profoundly universal. And in this poem, the "I" is also "you."
Subject matter and form
Obviously, grass is the major symbol in the poem, and you need to understand its various meanings to the poet. The form of the poem is a journey of the self as it encounters the world of people and nature, taking them into the self and gradually transforming and growing. Look at the various encounters and what the poet learns from each, as well as how his identity is challenged as it is transformed. Also, the style of the poem is distinctive and romantic, using rhythm, sound, multiple images (in the "catalogs," such as stanza #15), frequent participial verbs, and much repetition of structure and idea, as essential to the "song" and meaning of the poem. You should consider how any of these formal qualities are essential to the poem's meaning.
The reader
There are two main characters in this story--the poet and you, the reader. Look carefully at the relationship that the poet establishes with the reader and how it develops throughout the poem. He makes promises to the reader and he "projects" the reader--explain that.
Here's a student rereading paper of the second stanza which you might find inspirational.