Its alright I used this for my assessment, and think I did pretty good. I didn't talk much of it, because there was a limit.
I could have add a lot more. In the assessment it is important to state how it relates to imaginative journey, and what and how is the imaginative journey being represented.
The purpose is to show that god and his creatures are connected. The fact that the story has a purpose is emphasised by having Coleridge himself represent the the Mariner, and the audience represent the guest; these representations are continually reminded to the audience by the constant interruptions in the poem by the guest. "He prayeth well, who loveth well, both man and bird and beast" represents the purpose that Coleridge had want the audience to learn.
There are heaps of techniques in this poem, and there are helpful notes in the resource area. You should have a look at them.