Class worksheet on grammar and usage from David Foster Wallace, given to students of a nonfiction workshop he taught. The discussion in the comments is worth your time, too.
I liked this bit from the Answers and Explanations page on how Wallace taught the placement of modifiers.
You have been entrusted to feed for your neighbor’s dog for a week while he (the neighbor) is out of town. The neighbor returns home; something has gone awry; you are questioned.
“I fed the dog.”
“Did you feed the parakeet?”
“I fed only the dog.”
“Did anyone else feed the dog?”
“Only I fed the dog.”
“Did you fondle/molest the dog?”
“I only fed the dog!”
(via kottke)