Learn Limerick Meter
While a limerick can break rules of grammar and usage -- and social propriety -- it contains five lines and keeps to a set rhythm of either anapestic ("I must eat all the turkey alone") or amphibrachic meter ("There once was a woman from Kent"). The first line of the poem generally establishes the subject and often puts him into context by mentioning place, such as Edward Lear's "There was an old man of Hong Kong."
Learn The Rhyme Scheme
The rhyme formula of a five-line limerick follows the pattern of aabba. The last line is often a repetition of the end word of the first line, though it doesn't have to be. Generally the most favored limericks offer a surprise at the end, and often this can be a grammatical surprise, such as: "There was a girl from Bryn Mawr / who decided to visit a bar. / She got very drunk / and left with some punk / and now we don't know where she are." The middle lines of bb rhyme are often a shorter couplet to connect the beginning lines to the last line's punch, and they keep the momentum going with their pith and pace.
Write Transgressive Content
Many limerick aficionados, such as Gershon Legman and George Bernard Shaw, argue that a clean limerick is missing the point entirely. A limerick doesn't have to be bawdy to be successful, but a good limerick is often appreciated for being irreverent and often transgressive. The point is to violate taboo and walk to the edge of social convention.
Learn From The Masters
As with any genre of writing, you can best learn from its masters. Edward Lear is hailed as king of nonsense -- he even wrote books with the word "nonsense" in the title. An artist and poet, Lear popularized the limerick form during the serious Victorian era. He wrote a series of poems like this: "There was an Old Man with a beard, / Who said, 'It is just as I feared! / Two Owls and a Hen, / Four Larks and a Wren, / Have all built their nests in my beard!'" When you peruse the slew of famous writers who veered into silly territory, you'll develop a keen ear for quality limericks -- because, no, they are not all created equal -- and will be able to enjoy creating your own. Your limericks might not bring you literary fame, but they'll make you a hilarious party guest.