Proper Grammar isn't THAT critical in marketing copy, but... Readability is.
By now you know that following instructions from your high school English teacher will cause you to write dry, dull, uninspiring copy. Being "too proper" just makes your words sound stiff.
At the same time, being too casual makes you sound a little demented. And I HAVE seen it done. In fact, I've received emails with a subject line that went something like: "YO! Man! You Gotta Dig This!"
Uh - no, I don't gotta.
Many of us here have written about using the wrong word. Like saying "reigns" when you mean "reins" and "there" when you mean "their."
But there's another common error that I'm seeing more and more lately.
It's the over-use or mis-use of commas.
I tend to over-use commas myself when I think it sounds right. My more grammatical friends tell me you don't need the last comma when you write something like "Web pages, newsletters, postcards, and ezines." But I happen to think it sounds right, so I do it.
But now I'm seeing blog posts with commas that really mess up the flow.
Look how difficult it is to read this:
By now you know, that following instructions, from your high school English teacher, will cause you to write dry, dull, uninspiring copy.
This one is SO easy to avoid. Here's the trick:
After you write a sentence or a paragraph, read it out loud. Pause at every comma. If it sounds like normal conversation - great. If it sounds choppy or clunky or halting (as if you were really not sure about what you wanted to say) get rid of a few commas.