If you want to make your writing sound dull and hackneyed, using passive voice is probably the fastest way to do it.
In grammar, “voice” basically has to do with whether the subject of a sentence is doing something or having something done to it. English verbs can have two voices:
Active voice — The verb form you use when the subject of the sentence is doing something.
Passive voice — The verb form you use when the subject of the sentence is having something done to it.
Voice is difficult to define without using a lot of linguistic jargon. Fortunately, the concept is pretty easy to understand once you see a few examples, so let’s dive right in.
Active: Carly Rae Jepsen released a cover of “Both Sides Now.”
Passive: A cover of “Both Sides Now” was released by Carly Rae Jepsen.
Active: Canada rejected the U.N.’s demand for an apology.
Passive: The U.N.’s demand for an apology was rejected by Canada.
Active: The president sent troops into British Columbia.
Passive: Troops were sent into British Columbia.
When I taught sophomore English, I always told my kids that passive voice is what you use when you’re trying to get yourself out of trouble, and active voice is what you use when you’re trying to get somebody else in trouble.
Passive: Mom, the window got broken.
Active: Mom, Ryne hit a baseball through the window again.
See the difference? Politicians use passive voice a lot to deflect blame for crappy decisions. Kids use it to deflect blame for mistakes. Grad students use it to sound smarter than they really are. It’s a weaselly way of writing. At best, it makes you sound prissy; at worst, it confuses your reader.
Try rewriting these sentences in active voice:
1. Plastic lightsabers were purchased for the boys by their Aunt Emily.
2. Marjorie’s cell phone was hacked by some pervert.
3. I was hit by a foul ball while ogling the third-base coach’s backside.
4. The body was discovered by a newspaper carrier early Tuesday morning.
5. My patience was tested by his constant use of passive voice.
Incidentally, one of the best riffs I’ve ever read on passive voice was from a book called How to Write a Romance and Get It Published. I know we’ve already established that steamy love scenes are more trouble than they’re worth, but if you can score a copy of the book somewhere, read the chapter called “Beware of the Pillaging Mouth.” The author, Kathryn Falk, offers a brilliant (and hilarious) explanation of why passive voice is the enemy of good writing.
Emily
Red Fork Hippie 
I sort of get the difference (The Air Force’s Tongue and Quill did a good job of beating active and passive into my head), but I still don’t understand why passive is not as desirable. Why is that considered poor writing?
As its name suggests, passive voice is — well, passive. Instead of *doing* something, the subject of the sentence is having something done to it, which is boring. It’s also vague, and vague writing is never good writing — the purpose of writing is to communicate, and if you aren’t communicating clearly, you confuse your reader. Sometimes there’s a reason for being vague, but that reason is usually weaselly (“Mistakes were made” vs. “I made mistakes,” for instance). You can make a passive sentence specific, but you have to add extra words to do it: “Mistakes were made by me” vs. “I made mistakes.” Remember Mrs. Turner’s constant admonitions to “tighten your writing”? Swapping passive voice for active voice is a fast way to tighten your writing while making it clear and assertive. Passive voice tends to sound prissy and namby-pamby, which is seldom desirable.