Numerous writing guides (and, judging from the people I encounter, hundreds of writing teachers) drum it into student’s heads
that the passive voice is to be avoided at all costs to avoid the passive voice at all costs. That’s not always bad advice, but, as with most grammar “rules,” it’s a guideline rather than a commandment carved in stone.
First things first: Passive voice is a perfectly legitimate part of English (and most other languages). Using the passive voice is not a grammar error.
Next: Before you rail against the passive voice, know what it is. Intransitive verbs are not passive voice, nor are (necessarily) auxiliary verbs. Passives can occur only with transitive verbs (that is, verbs that can take a direct object). So even though the sentences This appears to be the right book or Something seems peculiar here may look “passive” because no action is happening, they’re not passive voice–they just have intransitive verbs. (For more on how to tell whether a verb is passive, zombies can help.)
Passive-voice sentences are often wordy or indirect. They can also be deliberately vague: Mistakes were made. The window was broken. No one gets the blame in these sentences.
However, just because a sentence is in passive voice doesn’t mean it’s wordy or vague. Sometimes the thing or person the action is being done to is more important than the person or thing that did it, so it should start the sentence. For example: The escaped serial killer was caught and taken back to prison after a 12-hour search. We can assume law enforcement was responsible for apprehending the fugitive. But the most important thing is that a murderer is no longer on the loose.
As usual, what this boils down to is being clear and direct. Often you want the active voice for that. But sometimes, the passive voice gets the job done more effectively.
Better advice for avoiding wordiness and being more specific is to watch out for dummy subjects and smothered verbs.