Being a professional copy editor, I spend way too many of my waking hours trying to make what other people write as clear as I can. Most hurdles that trip up authors involve switching from spoken word to written word. The rules (or guidelines or what have you) for written English are different from the rules for spoken English (another post, another time), but some authors have trouble making the switch.
One of the most common corrections I make is the placement of the word only. Normally, people just place it right before the verb, but that isn't always the right place. Only should appear as close to the word or words it modifies as possible. (Even though only ends in -ly, it isn't always an adverb.) Consider these permutations of "I ate the apple."
Only I ate the apple. "I was the only one to consume this delectable fruit."
I only ate the apple. "Bob juggled with it, and Jane did a magic trick with it, but I just ate it."
I ate only the apple. "Out of this entire smorgasbord, the only thing I ate was the apple."
I ate the only apple. "There was only one apple, and now it's in my belly."
I ate the apple only. "I didn't touch your damn pear!"
Now, "I ate only the apple" and "I ate the apple only" seem mean the same thing, but there is a subtle difference. Say the two sentences out loud and listen to where you put the emphasis. You'll probably hear this:
I ate only the apple.
I ate the apple only.
In the first sentence, the stress in on only -- on the apple's solidarity; in the second sentence, the emphasis is on apple; as opposed to the other fruits. These two sentences could answer two different questions:
Did you eat much? No, I ate only the apple.
Did you try one of the peaches? No, I ate the apple only.
Of course, there are sure to be exceptions the "rule" about putting only next to the word it modifies. If only I could come with a good example of one of them . . .