1. Shakespeare compares her qualities to things that are unrealistic standards.

Eyes: They are nothing like the sun.

Lips: Coral is far more red than hers.

Cheeks: Her cheeks aren't as pink and beautiful as a mixture of roses.

Breath: Her breath isn't as sweet as perfume.

Voice: Music is more pleasing than her voice.

2. He compares her to a goddess. A goddess gives the image of poise and elegance. When his mistress"treads" he means that she steps and walks unlike a goddess would.