I tended to just link them together quite loosely, and then expand on the theme highlighted by analysing Blake’s work alone to ensure focus was kept on his poetry (it can be quite easy to get carried away otherwise I think). So, for example, you could say something like:
Both poets attempt to convey the perils of distance through nature (you could mention one short example from your unseen poem e.g ‘name of poet demonstrates this with the line...). However, Blake’s reasons for this can be attributed to wanting to distance himself from what he perceived as the evils of Georgian England. His poem London begins ‘I wander through each charter’d street/ Near where the charter’d Thames does flow’. The speaker of the poem, the ‘I’, can be interpreted as Blake himself, despairing of the rest of London’s inhabitants, particularly those who believe they can own nature (this being illustrated through the description of the Thames as ‘charter’d’, which Blake presents as an alien idea through the contrasting description of the flowing river). In the original version of the poem, Blake had written ‘dirty’ in the place of ‘charter’d’, demonstrating the extent of his disgust towards this idea of ownership, the repetition of the word in the final version however, perhaps reflects despair over how prevalent Charters had become. Whilst Blake’s description can be interpreted as reflecting the ideas demonstrated in the work of Burke and Paine (Paine described charters as ‘a perversion’) it also arguably illustrates a loss of freedom as a result of the disruption and ownership of nature.
I’m sorry that’s quite tenuous- it wasn't the best quote for nature but I was sort of going on what I could remember. I hope it gives you an idea of how to structure your essay though
I think you can pick any poem for your unseen, but I am far from certain, so the best bet is to check with your teacher.
With regards to the Tempest, try and get a stage direction and a prop integrated with your analysis- it's really important to talk about it as a play.
Hope that helps