1. Muse: i.e., poet.

2. Stirr'd: inspired.  a painted beauty: a person who uses cosmetics to appear beautiful; i.e., a false beauty.

4. every fair with his fair doth rehearse: compares his fair lady with every fair thing.

5-6. Making a couplement of proud compare, / With sun and moon: i.e., joining (his fair lady) in a proud comparison with the sun and moon.  —In the second quatrain (lines 5-8) Shakespeare uses overblown language to mock the overblown rhetoric of conventional poets.

8. rondure: —A fancy word for "sphere."  hems: encompasses.

9. but: only.

12. those gold candles fix'd in heaven's air: i.e., stars.  —The comparison of a beautiful lady to a star was a convention of the love poetry of Shakespeare's time; Shakespeare himself does it in Romeo and Juliet.

13. hearsay: conventional or trite expressions.

14. I will not praise that purpose not to sell: since I don't intend to sell, I will not praise.  —I think this final line is a real stinger, because the poet seems to be saying that only pimps extravagantly praise their ladies.