Often poetry will have a specific rhythm to its phrases - even though it isn't set to music. How is this possible? Let's look at a couple of classic examples, in which you should hear a definite beat.
Rhyme Scheme
Ah me! I see him on the cliff! A - 8 pulses
Farewell, farewell to hope, B - 6 pulses
If he should look this way, and if A - 8 pulses
He's got his telescope! B - 6 pulses
To whatsoever place I flee, C - 8 pulses
My odious rival follows me! C - 8 pulses
For every night, and everywhere,
I meet him out at dinner;
And when I've found some charming fair,
And vowed to die or win her,
The wretch (he's thin and I am stout)
Is sure to come and cut me out!
(excerpt from Size and Tears, from Phantasmagoria and Other Poems by Lewis Carroll)
I went into a public 'ouse to get a pint o' beer,
The publican 'e up an' sez, "We serve no red-coats here."
The girls be'ind the bar they laughed an' giggled fit to die,
I outs into the street again an' to myself sez I:
O it's Tommy this, an' Tommy that, an' "Tommy, go away";
But it's "Thank you, Mister Atkins", when the band begins to play,
The band begins to play, my boys, the band begins to play,
O it's "Thank you, Mister Atkins", when the band begins to play.
(excerpt from Tommy, from Barrack-Room Ballads by Rudyard Kipling)
Now let's assume there's a place in your lyric where there is some action or something of a climax. To accent this you might use shorter phrases, and intensify the rhyme scheme (both internal and end-of-line). Your whole song might be written like this, if it's really action-packed. This is a great example of that:
Rhyme Scheme
Baby, here I am, - (non-rhyme)
I'm a man on the scene. A
I can give you what you want -
but you got to go home with me. A
I've a got some good old lovin', -
and I got some in store. B
When I get through throw in' it on you, -
you got to come back for more. B
Boys and things will come by the dozen,
but that ain't nothin' but drugstore lovin'
Pretty little thing, let me light your candle,
'cause mama I'm sure hard to handle, now, yes I am.
(excerpt from Hard to Handle, by Alvertis Isbell, Allen Jones & Otis Redding)
Besides the obvious rhymes, take a look at all the internal/ implied rhymes: here I am/man on the scene, what you want/but you got, dozen/nothin'/lovin', pretty little thing let me light (alliteration with T's and L's). Even when reading this lyric aloud, you can feel the implied quickness!
In the above examples there is a combination of techniques employed to achieve this rhythmic inference.
1) End-of-line rhymes.
2) If we're talking verses (as in the Carroll example), they're each the same number of lines (and in this case, the rest of the poem continues in 6-line verses).
3) Pulses: Instead of referring to the number of syllables per line, I'm going to call them pulses, because often when singing or speaking English you will find yourself "squeezing" or shortening syllables to make them fit neatly into the rhythm you've already established in your head. Think of these like musical beats, where you may have several notes (or syllables) in the time of one count. I've marked the number of pulses I hear in the Carroll poem. In verse 2, because you're now probably expecting the pulse scheme to continue, you'll instinctively read the words "dinner" and "win her" more quickly, to make them fit into the expected 6-pulse rhythm.
4) Internal rhyme and alliteration. Internal rhyme can be direct, as in...
There was no light at all, at all; I wint from tree to tree, And I called him as his mother called, but he nivver answered me.
(from The Convalescent, by Robert W. Service)
...but is more commonly an implied rhyme by duplicating vowel sounds, either within one line (as in the Hard to Handle example) or within a group of lines.
Poetry often consists of a number of verses or stanzas of equal length and similar rhythms. Specific parts of a lyric, however, are by nature designed to achieve specific and unique functions. Usually, these are...
verses provide the plot. Generally speaking, all the verses in a song should share the same form/rhyme scheme.
choruses provide the summary or theme of the song. Usually the chorus is identical each time it's repeated, but sometimes there are minor variations.
bridges often share new information and can be a total departure from the verse & chorus. (As can instrumentals.)
As these are three distinct sections, the change from one to the next is usually indicated by a new chord progression, and/or changes to the rhyme scheme, number of lines in the section, and length of the phrases.
Of course, listeners also tell which is the chorus, and which is the verse, by things like vocal harmonies, change in instrumentation, production, etc. But these things are added after the song is written. Your song should have distinct sections waaaay before it gets to the "studio-tweaking stage"!
Note the use of rhyme and alliteration in the following verse, and how the chorus is a definite change in rhythm...
My love is the evening breeze, touchin' your skin
The gentle, sweet singin' of leaves in the wind
The whisper that calls after you in the night
And kisses your ear in the early light...
And you don't need to wonder, you're doin' fine...
And my love, the pleasure's mine...
Let me go crazy on you...crazy on you
Let me go crazy, crazy on you...oh...
(excerpt from Crazy on You, by Heart)
Read your lyrics to yourself and see if you can tell the difference between your sections by metre alone (not considering the lyrical meaning).
I'm not implying that you should constrain yourself to a standard rhyme scheme, like ABAB, although those work pretty darn well in most lyrics (especially country...as below). Because if you do, you have to be on your toes so that your lyrics do not become predictable.
If I could grant you one wish
I'd wish you could see the way you kiss
Ooh, I love watching you baby
When you're driving me ooh crazy
Ooh, I love the way you
Love the way you love me
There's nowhere else I'd rather be
Ooh, to feel the way I
Feel with your arms around me
I only wish that you could see
The way you love me, the way you love me
(from The Way You Love Me, by Keith Follese & Michael Delaney)
A more complex or subtle rhyme scheme is sometimes desirable, so the listener will be less able to finish your sentences for you (and thus become bored).