The beginning of your analysis of Geoffrey Hill's poem "Genesis" should focus on the title. The title is an obvious allusion to the Biblical book of Genesis. Two aspects of the Biblical story are important. The first is the account of God's creation of the world, including the physical earth (both land and water) and the animals and humans that populate it. The second important aspect of the Genesis story for the poem is the concept of Adamic naming, in which Adam gives names to the creatures populating the world. Hill here is using a common trope in which the poet's act of naming in the poem is seen as parallel to Adamic naming. Just as God's creatures are in the image of God, so Adamic naming is an image of the act of creation. The poem is structured to follow the six days of Creation as set forth in the Biblical story.
On a formal level, you should examine the meter of the poem. Although the base meter is iambic tetrameter, there are several rhythmical variations in the lines. Although most lines of the poem are rhymed, there are several instances of variation in rhyme pattern and use of slant or off-rhymes you could discuss. The first couplet, for example, uses slightly different vowel sounds, but the subsequent quatrain uses perfectly regular rhyme sounds.