Although some basic rules apply in making singular words plural, there are exceptions. The most effective method is to learn the most commonly used rules and to keep a list of words that exemplify each rule. The exceptions have to be memorized.
The Most Common Rule
Know and apply the most common rules. For example, most nouns are made plural by adding -s to the word. Add -es to nouns ending with -ch, -sh, x, z, and s.
Memorize the rules for words that end in specific letters. For example, if a word ends in a consonant and a -y, you'll need to change the -y to an -i and add -es. Words that end in -f or -fe usually change the -f to a -v sound and end in -ves.
Familiarize yourself with the spellings of the most common irregular plural nouns. Some, such as deer and sheep, don't change at all. Some change vowel sounds, such as man/men, woman/women, goose/geese, or tooth/teeth. Some have letters added to the end, such as child/children and ox/oxen.
Know when to use an apostrophe to make a singular noun plural. Add an apostrophe when writing the plural form of a word that refers to the word itself, like "The teacher told me I used too many and's in my essay". An apostrophe is also used when making letters plural as in "He made three A's and four B's on his report card."
When in doubt, check the noun's plural form in a dictionary. Occasionally, you will see more than one accepted spelling of the word. In those cases, use the form that is listed first.