A problem I run into all the time with both my own writing and other people's is that some text can be read more than one way, and sometimes the various ways have different meanings. This kind of ambiguous writing can be easy to spot, as in the following example:
Susan told Kelly she didn't know where her shoes were.
You can see the problem. Whose shoes are we talking about, Susan's or Kelly's? On top of that, who is the first "she" referring to? You could mean:
Susan told Kelly that Kelly didn't know where Susan's shoes were.
(As some strange kind of insult, I assume. "You're so dumb, you don't know where my shoes are!")
Most writers can spot these kinds of mistakes and fix them almost as soon as they're written. But here's a subtler one I ran across on Slate, a news/opinion site:
We disparage things we don't approve of as phony.
Here's the article I saw it in if you're interested.
I can tell the author's trying to say that if we disapprove of something, we call it phony. But can you see the other way to read it? Try this:
"If we don't approve of the level of phoniness in something, we disparage it."
I know the author doesn't mean us to read the sentence that way. But you'd be surprised how many times I run into contest entries that contain a sentence that could be read more than one way. When that happens, I can guarantee you the author doesn't want anyone reading the sentence the other way.
I can also guarantee that if you have enough readers, some small percentage of them will read it the wrong way.
Here's how I'd revise the Slate sentence:
If we disapprove of something, we disparage it as phony.
So, when you're writing, read over your material once in a while and try to deliberately misunderstand it. If you find you've written something that's easy to draw unintended conclusions about, consider rewriting it to make your intention clearer.