"Jenny was being served her apple martini by the bartender just as the front window was shattered by a speeding Humvee, and Jenny was thrown from her stool."

OR

"The bartender was serving Jenny her apple martini just as a speeding Humvee shattered the front window and threw Jenny from her stool."

Which sentence jumps off the page? Notice that I didn't alter a single word, aside from changing each verb from passive to active voice.

If you haven't heard those terms before, here's a simple definition: Passive voice makes the subject into the (passive) object of the verb. Active voice means the subject is the (active) person or thing performing the action of the verb. In the second clause, the window isn't doing the shattering--the Humvee is. The window is the object of the shattering. So shouldn't the Humvee be the subject? Ancient grammar swamis say yes.

But, you say, the sentences don't seem that different to me. Wrong. Try this: count the words. Okay, fine, I'll do it for you. The first example contains 28 words, the second 23. Multiply that difference (five, math whiz) by the number of sentences in a manuscript. My example was extreme, so let's be conservative and say you save one word every fifth sentence by going through your manuscript and changing as many verbs as you can from passive to active.

Take a manuscript of 300 pages, with an average of 300 words per page, and sentences of about 10 words' that's 9,000 sentences. Wow. No wonder finishing a manuscript is hard. Result: you've just cut 1,800 words, or six pages, from your manuscript.

Why would you want to cut six pages from your magnum opus? Maybe you don't. Maybe you want to fill those six pages--or twelve, if you're one of those ambitious people who writes 600-page manuscripts--with useful information about plot, character, or theme, instead of useless words such as was, were, by, and that annoying suffix "-ing." But it's okay to simply cut. Honest. Quality is more important than quantity.

Even if you don't see the difference in my one example, use active verbs consistently and your writing will pop as it never did before. The reason is self-explanatory: it's more active, and useless words aren't bogging it down. Repeat after me: useless words are bad words.
The Exception That Proves the Rule

F. Scott Fitzgerald used the passive voice. I'm sure of it. But when he did, I'll bet he had a good reason. My example might be taken from a novel in which Jenny is the protagonist. Her true love, perhaps, is driving the Humvee. (The Humvee is not 'being driven by' her true love.) So Jenny, not the bartender, should be the focus of the sentence. With this rule, as with all others that are meant to be (occasionally) broken, always be aware of why you're breaking it.

You've gotta know the rules before you can know how to break them. And no one knows all the rules. Not even me.