The first two lines of "London" feature repetition, a literary device Blake uses several times in this poem. The word "charter’d," meaning "mapped," is repeated, showing that the city is mapped out in a way that is characteristic of urban life. This type of restriction is in contrast to the freedom of the countryside. In the next two lines, the word "mark" is repeated three times as a means of emphasizing the way in which the polluted city marks its inhabitants. In the following stanza, the word "cry" is repeated (and "cry" also appears in the third stanza), as is the word "every." The repetition of the word "cry" emphasizes the suffering of both adults and children in London. The repetition of the word "every" is a form of anaphora, which is the repetition of a word at the beginning of phrases that follow each other, and it serves to emphasize how this suffering characterizes everyone the poet sees in the city. Many phrases in this stanza also start with "in," another example of an anaphora.
In the third stanza, the words "Church" and "Palace" are synecdoches--the substitution of part of something for its whole. For example, "Church" stands for religion, while "Palace" stands for the monarchy. Both of these institutions are oblivious to the cries of the people around them.
In the last stanza, the phrase "Marriage hearse" is a kind of oxymoron, or a joining of contrasts. The idea behind this phrase is that the infant is born to a mother who is a prostitute and curses her newborn child. The child's birth is both a marriage, or the result of a sexual union, and a death sentence, as the woman has a plague. Therefore, even birth brings with it the taint of death in "London."