Double the ending consonant if the word is one syllable, has one short vowel, one ending consonant and you are adding a suffix, such as "ing," "ed," or "er." For example, the word "bed" is one syllable, has the short vowel sound "eh" and ends in the consonant d. If you were to add the suffix "ing," it would become "bedding."
Double the consonant if the word has a CVC pattern, when adding the suffix "ing" or "ed." For example, "rub" has a consonant, vowel, consonant pattern and would be spelling "rubbed" when adding the suffix "ed."
Double the consonant in a two-syllable word if the second syllable is stressed. When adding the "ing" or "ed" suffix to a two-syllable word check to see if the second syllable is stressed before doubling the consonant. For example, in the word commit, "mit" is stressed and the word would be spelled "committed" when adding the "ed" suffix. However, in the word visit, "vis" is stressed so the "t" does not get doubled when adding a suffix.