Verse and Prose
Cymbeline, like Shakespeare's other plays, is written in a combination of verse (poetry—some of it rhymed) and prose (how we talk every day).
Verse
In most of Shakespeare's plays, a lot of characters speak in unrhymed iambic pentameter (also called "blank verse"). Don't let the fancy names intimidate you—it's pretty simple once you get the hang of it.
An "iamb" is an unaccented syllable followed by an accented one. "Penta" means "five," and "meter" refers to a regular rhythmic pattern. So "iambic pentameter" is a kind of rhythmic pattern that consist of five iambs per line. It's the most common rhythm in English poetry and sounds like five heartbeats: ba-DUM, ba-DUM, ba-DUM, ba-DUM, ba-DUM.
Let's try it out on these lines from Cymbeline:
You DO not MEET a MAN but FROWNS: our BLOODS
No MORE oBEY the HEAvens THAN our COURTIERS
Every second syllable is accented, so this is classic iambic pentameter. Poets (and playwrights) hardly ever write in perfect meter, because perfect meter sounds like a nursery rhyme. Varying the meter draws attention to certain words and helps the verse sound a little more natural.
That takes care of iambic pentameter. Since these lines have no rhyme scheme ("bloods" and "courtiers" don't rhyme), we call it "unrhymed iambic pentameter," which is also known as "blank verse."
Blank verse is a pretty formal way to speak, so it's usually reserved for nobles and formal situations in Shakespeare's plays.
Broken Lines
Shakespeare also drops little hints about his characters with his writing style. Did you notice that the Queen never really seems to have full lines? That's what we call broken lines. It's when a line of verse doesn't come to a complete end. In iambic pentameter, each line is supposed to have 10 syllables. But not all do.
Sometimes this is just comes down to the topic and the other words in the line—after all, it's pretty darn hard to write in perfect iambic pentameter all the time. Not even Shakespeare does it totally consistently. But when this happens again and again with one character in particular, we know it's more than just an accident.
Now, the Queen's lines are totally like this. Check out what she tells Imogen here:
This hath been
Your faithful servant. I dare lay mine honor
He will remain so. (1.2.214-216)
So what's the deal? Well, maybe these broken lines show the Queen's nervousness or anxiety. After all, these lines can be said more quickly than complete lines could. The stop-and-start nature of the lines might mean she's out of breath or quickly uttering her lines.
Prose
Now that we've gone over verse, let's tackle prose. Characters who don't get to speak in verse just talk. Take Cloten's lines when he searches for Imogen in Wales, for example:
I am near to the place where they should meet,
if Pisanio have mapped it truly. How fit his garments
serve me! Why should his mistress, who
was made by him that made the tailor, not be fit
too? (4.1.1-5)
See how there's no pattern to the lines? That's because he's just talking; there's no meter involved. What's that called? Yup: prose.