I've been given London by William Blake to analyse for homework but I'm really struggling. There really aren't that many devices in it. My question is, how does William Blake present powerlessness in London?

You're right, there aren't that many devices in London. That's not a problem, though. 

Your question gives you a lot of help. You're looking for powerlessness and how it's presented. So let's find an example. 

In the first stanza, you find an example in the fourth line: "Marks of weakness, marks of woe." We know this is an example of powerlessness because weakness is very close in meaning to powerlessness. 

So how do we analyse it? 

Well, let's look at it in a bit more context, zoom out a little. Have a look at where he's seeing it: "in every face I meet" and in "each...street." This suggests that this form of powerlessness is very widespread at the time. 

So how does it present it? As a mark of weakness on people's faces. The work mark in the context of a face suggests a blemish, a scar or perhaps even a pock mark on a person's face. This has connotations of disease. 

Think again about how widespread it is: very. It's a visible mark on everyone's face, in every street. It's almost as if he's suggesting that powerlessness in London is an epidemic, a disease of kinds. 

So we can make a point out of that, like this:

Blake presents powerlessness in terms of it being a widespread disease or epidemic. This is evident in his choice of language when he first encounters it, noticing it in "every face [he] meet[s]" as "marks of weakness". Finding it in every street and in every face suggests the broad, epidemic-like proportions of the spread of powerlessness, whilst the idea of weakness or powerlessness manifesting on a person's face as a "mark" has strong connotations of pox, scarring or disease. Blake's pathologising of disease implies further that the condition is growing and requires a public health intervention just as a plague would, but also that it is something to be feared, that it can catch very easily. Anyone, as he makes very clear, can be vulnerable to it. 

Can you see any other evidence of language in here that suggests that it is widespread or epidemic like? Maybe consider how many different people it affects in the second and third stanzas? Can you see any other evidence of powerlessness taking on disease-like properties? Any other language referring to the idea of disease? And what does Blake identify as the cause of said disease? 

Please contact me if you want any further advice.