A lot of students analyse individual poems in an exam essay but what puts you in the highest bands and helps you to achieve higher marks is the way you compare and contrast the poems. It's important to look out for noticeable similarities or differences in their themes, contexts, characters and characterisation and literary devices; this is similar to how you would break down an individual poem but you must learn to keep both in mind at the same time so you can discuss them in tandem to one another. Often students write half an essay about one and the second half about the other, but if you are able to interweave them and make general, as well as explicit links this demonstrates a higher level of understanding and sophistication. If you can also discuss the poets' intentions with respect to why the poems may be similar/different that adds further complexity.