Twenty examples is a lot to ask for, but I will give you six, and hopefully you can find the rest yourself.
Montag uses a lot of similes to describe Clarisse. For example, he says that her face is as "bright as snow in the moonlight," implying that she is radiant and that she has a beauty which seems to glow. Montag also describes Clarisse's face as "like the dial of a small clock seen faintly in a dark room in the middle of a night." This simile seems to suggest, again, that Clarisse represents a glimmer of light in the darkness and perhaps a promise of better, brighter times to come. One of the reasons Montag is attracted to Clarisse is because he sees in her much of himself and because she makes him reflect on his own life. This is perhaps why Montag says, again using a simile, that her face is also "like a mirror."
Bradbury also uses similes to describe the protagonist, Montag. For example, Bradbury writes that Montag "wore his happiness like a mask." The implication here is that the happiness that Montag projects is a fabrication and a pretense. He wears this mask because it is safer to appear happy. Beneath the mask, however, he is of course not very happy at all.
About a third of the way through the story, there is a passage describing Mildred, Montag's wife, in a particularly sinister manner. Her body is described, using a simile, to be "as thin as a praying mantis from dieting," and her "flesh" is described as "like white bacon." Mildred personifies society's standards of beauty. Mildred starves herself to look thin, and she seems pallid and ill as a consequence.