The metrical pattern of Shakespeare's Sonnet 130 is actually perfect iambic pentameter all the way through. An iamb is two syllables together, one with soft and one with hard accents. Iambic pentameter is a line of five iambs. Sonnets are traditionally written in iambic pentameter, and Sonnet 130 does not break this pattern, as we see in the second stanza:
I have' / seen ro' / -ses dam' / -ask'd , red' / and white',
But no' / such ro' / -ses see' / I in' / her cheeks';
And in' / some per' / -fumes is' / there more' / de -light'
Than in' / the breath' / that from' / my mis' / -tress reeks'.
However, that being said, there are a couple of unusual choices in the meter that may throw the reader off. For instance, in American English the word "coral" is typically stressed on the first syllable: cor' al. However, in line two, Shakespeare stresses the second syllable of coral:
Co -ral' / is far' / more red' / than her' / lips red'
We must remember that some pronunciations for Renaissance Early Modern English are unknown to us. In that time period, the second syllable may have been drawn out farther than it is today due to the spoken accent.
Another spot that looks unusual is where he accents the preposition "on" in line 12:
My mis' / -tress, when' / she walks',/ treads on' / the ground'
This is unusual because normally in English, we would emphasize either a noun, a verb, or an adjective, rather than a preposition. However, being that both "tread" and "on" are monosyllabic words, even this pair is a perfect iamb, which maintains his consistent use of iambic pentameter.