Know an appositive when you see one.

An appositive is a noun or noun phrase that renames another noun right beside it. The appositive can be a short or long combination of words. Look at these examples:

The insect, a cockroach, is crawling across the kitchen table.

The insect, an ugly cockroach, is crawling across the kitchen table.

The insect, an ugly cockroach with hairy legs, is crawling across the kitchen table.

The insect, an ugly, hairy-legged cockroach that has spied my bowl of Frosted Flakes, is crawling across the kitchen table.

Here are more examples:

During the dinner conversation, Clifford, the messiest eater at the table, spewed mashed potatoes like an erupting volcano.

My 286 computer, a modern-day dinosaur, chews floppy disks as noisily as my brother does peanut brittle.

Genette's bedroom desk, the biggest disaster area in the house, is a collection of overdue library books, dirty plates, computer components, old mail, cat hair, rough drafts, and McDonald's happy meal toys.

Reliable, Diane's eleven-year-old beagle, still chews holes in the living room carpeting as though he were a puppy.

Punctuate the appositive correctly.

The important point to remember is that a nonessential appositive is always separated from the rest of the sentence with comma(s).

When the appositive begins the sentence, it looks like this:

A hot-tempered tennis player, Robbie charged the umpire and tried to crack the poor man's skull with a racket.

When the appositive interrupts the sentence, it looks like this:

Robbie, a hot-tempered tennis player, charged the umpire and tried to crack the poor man's skull with a racket.

And when the appositive ends the sentence, it looks like this:

Upset by the bad call, the crowd cheered Robbie, a hot-tempered tennis player who charged the umpire and tried to crack the poor man's skull with a racket.