Romeo uses two similes to describe Juliet’s extraordinary beauty. The first simile is deployed in the lines

It seems she hangs upon the cheek of night As a rich jewel in an Ethiope’s ear.

In these lines, the phrases ‘cheek of the night’ and ‘Ethiope’s ear’ apparently refer to the darkness of the night personified as an African/Ethiopian lady. As we know, an African lady is black in complexion. Juliet stands out conspicuously amidst others in the dark night, lit up by torches in the room. There is a stark contrast between the bright and shining complexion of Juliet and the dark night.

The second simile is deployed in the lines: So shows a snowy dove trooping with crows As yonder lady o’er her fellow’s shows.

In these lines, the comparison is between the ‘snowy dove’ and the ‘crows’. Obviously Juliet is the snowy dove and the other ladies in the room are crows. ‘Dove’ is a symbol of ‘love’ and beauty; crows have always been considered black and ugly. Naturally, for Romeo, Juliet is the personification of love and beauty. It also implies that the other ladies including Rosaline, with whom he had fallen in love, appear ugly and gross to him. That is why he uses the phrase ‘her fellows’, to describe them. These two similes highlight how enchanted Romeo is with her beauty.