If "The Passionate Shepherd to His Love" was one of the earlier poems you read in school, we're betting your teacher chose it because it's a great example of regular rhyme and meter. In this case, Marlowe writes in iambic tetrameter, which means he's got four iambs per line, making each line go daDUM daDUM daDUM daDUM. And he's got a pretty basic rhyme scheme: AABB.
Check this out:
And we will sit upon the rocks,
Seeing the shepherds feed their flocks,
By shallow rivers, to whose falls,
Melodious birds sing madrigals. (5-8)
With the exception of line 6, with starts off with a trochee ("Seeing" goes DAdum, instead of daDUM), this is pretty darn perfect iambic tetrameter. So perfect, in fact, it sounds more like a song than a poem.
The entire poem is composed of six four-line stanzas, or quatrains, just like the one above. Each quatrain is made up of two rhyming couplets, the majority of which are written in perfect iambic tetrameter and, if you use Renaissance-era pronunciation, rhyme perfectly.
Sure, most verses in tetrameter end up sounding a little sing-songy when read aloud, but Marlowe avoids this effect by peppering his lines with poetic devices that sneakily shake things up and steer clear of the nursery rhyme curse. Take a look at this couplet from the third stanza:
And I will make thee beds of roses,
And a thousand fragrant posies (9-10)
A perfect line of iambic tetrameter should end in a stressed syllable, but in line 9 Marlowe forces an extra unstressed syllable onto the end of the line (the -ses of "Roses"). You might think this would muck up the meter, but if you read the line aloud (go ahead, we're sure the other people in the library will find it inspirational), the extra syllable adds a little pizazz to the line without making it feel awkward or jarring.
Marlowe's substitution of a trochee (DAdum) for an iamb in line 10 works in a similar way; the changes create variety and texture within the meter, so the poem avoids sounding like Little Bo Peep, but still colors within the lines, too. He creates a metrical musicality that mirrors the springiness of the countryside in which the speaker wants his lover to live.