In passive voice, action verbs are paired with verbs of being, such as "is," "are," "am," "was," "were," "be," "being," "been," "has been," "have been," "had been," "will be" and "will have been." Get used to looking for these words in your sentences. Look for situations in which the verbs of being are combined with another verb, specifically a past participle, usually ending in "-ed." For instance, in the sentence "This house was designed by Tom," the "was" is followed by the past participle "designed" to form a passive sentence structure. In active voice, the sentence would read, "Tom designed the house."
Watch out for irregular verbs, whose past tense form does not end in "-ed." For instance, in the sentence "I was caught by my mother," the past tense form of "catch" becomes "caught" and when combined with "was" creates a passive sentence structure. In active voice, the sentence would read, "My mother caught me."
Ask yourself who is doing the action in your sentence and to whom the action is being done. Use the traditional sentence structure of subject-verb-object in your writing, such as in the sentence "I built the tree house." Avoid the passive construction, "The tree house was built by me." If you find you have written such a sentence, rewrite it in active form.