The most specific guideline within a clerihew poem is the rhyming formula, which consists of a total of four written lines. The first two lines rhyme with each other, and the last two rhyme with each other. This rhyming pattern (a-a-b-b) is what sets the poem apart from others, which are typically a pattern of a-b-a-b. The timing varies from short and snappy to long-winded silliness.
Another main point within a clerihew poem is that the first line must include the name of a well-known person. This is typically a famous person but can certainly be written for the particular circle of people who will be enjoying the poem, such as a classroom of children or an adventurous family.
The second line must end as a rhyme to the character's name from the previous line. For example: "The people of Spain think Cervantes (Line 1) Equal to half-a-dozen Dantes" (Line 2) ~ E. Clerihew Bentley. The rhyming and timing are both important factors within the first two lines, but they must also be comical or silly. The more ridiculous and whimsical, the better. The comedy should delight all who read the poem and not be cruel or mean-spirited in any way.
The final two lines of the clerihew poem tell a humorous commentary on the main subject and are decided by his personality traits and position within his surroundings. Depending on the character and general theme of the poem it can be a political insight, historical reference or downright absurd sociological observation. To continue the above-referenced poem by E. Clerihew Bentley himself: "An opinion resented most bitterly (Line 3) By the people of Italy" (Line 4).