How can I analyse Blake's poetry, when so much of it is very simplistic? There seems very little to say about it which isn't obvious.

It is understandable why any student would have this question. The simplicity of many of Blake's poems can make them intimidating to analyse. However, this simplicity is what makes them so rich in interpretive possibilities! Let us take 'The Blossom', from Songs of Innocence. This poem is made up of two very similar six-line verses, so a good place to start is with their differences. These will inform us about any differences in the significances of the sparrow and the robin. The most obvious difference is each bird's reaction to the "happy blossom". While the sparrow seeks their "cradle narrow / Near my bosom", the robin is heard "sobbing sobbing [...] Near my Bosom". As the poem's two verses are so similar, both in content and in form, this difference appears more stark and significant. Since the poem is so simplistic, this difference could be interpreted several different ways. For example, notice that the sparrow is "Merry Merry", while the robin is "Pretty Pretty". This difference could suggest that a happy, joyful outlook leads to a wholesome reaction to the joys of nature ("flying" near the speaker's "bosom"). On the other hand, beauty, or perhaps vanity, leads to a destructive, negative reaction to such joys ("sobbing" near the speaker's "bosom"). Do you find another interpretation more convincing? Remember to back up your assertions with textual evidence! Your answer does not need to definitively 'solve' any of Blake's poems, and even high-level academics who try to achieve this usually fail. Rather, it is enough to notice features of the poems, and present your examiner with your reading of the significance of these features.