On Rhythm and Meter, or, How do I Wrote Zeb? · 5:49pm Dec 11th, 2013
I've seen many people here comment on how hard it is to write dialogue for Zecora. I've given advice on an individual level before, but at this point, I'd like something to point to.
It's not simply enough for Zecora's dialogue (or that of any other rhyming character) to rhyme. You're literally writing poetry, and that means using rhythm. Let's analyze our main subject's first line in "Bridle Gossip":
Beware, beware, you pony folk,
Those leaves of blue are not a joke!
The underlined syllables are those that are emphasized. As you can see, each line has four iambs, metrical "feet" that consist of an unstressed syllable and a stressed syllable in that order. Thus, the line is iambic tetrameter, one foot per line short of Shakespeare.
The point to take away from this is that both ends of each couplet have to have the same number of syllables in the same rhythmic arrangement. There is a little leeway, of course; that's one form of poetic license. As long as it still sounds right, you can add or drop a syllable to a line, though contractions, filler words, and synonyms can also be used.
Note that you are not restricted to any particular style or foot. Feet come in every conceivable combination of two to four stressed and/or unstressed syllables, though disyllables, dactyls, and anapests are the most common. Combinations of different feet in a line can be done as well. All that matters is consistency; whatever rhythm you established in the first line must be repeated in the second, poetic license notwithstanding.
On the other hand, by working within the confines of a given meter, you can write song parodies. For example:
I am the very model of a modern major-general.
I've information vegetable, animal, and mineral.
Here we have a case of iambic octameter. (As a side note, Octameter Melody seems like an excellent name for Octavia's father...) Any new lyrics will have to fit the tune, and therefore, the meter, as these do:
I am the very model of a modern cartoon character
With sanity that's low enough to be fourth-wall aware-iter
I hope I've demystified the matter a bit for everyone. 
No, no, no, it's
I am the very model of a cartoon individual
My animation's comical, unusual, and whimsical
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I used one of mine.
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I see somebody watches Animaniacs...
Zecora's rhymes can be hard to find
Most writers seem to just simply have no time.
But patience given and time taken,
can bring about quite the sensation.
Alas I have not much patience,
So I'll end this now, without a rhyme... -ence.
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Without a cadence?
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I'll take it!
Thank you.
Came here to mention what I like to call the "Equestria, Buck Yeah" Rule, which is the awfully convenient fact that swapping "America" for "Equestria" won't affect any rhyme or meter,
It's been a year and a half, I'm pretty sure I can double post. Anyway, I was recently reminded that keeping time is canonically the main purpose of the Green Lantern Oath, so meter is especially important for parodies of that.