Add and remove commas to see how they affect the sentence. For example, "Let's eat, everyone" becomes "Let's eat everyone" - changing the meaning of the sentence from a pleasant call to dinner to an expression of cannibalistic tendencies.
Remove a colon from a headline and take a second look at the sentence. For example, "Spotted manatee found off South Carolina beach" becomes "Spotted: Manatee found off South Carolina beach." In other words, a headline proclaiming an amazing, undocumented animal is now about a rare but not unheard-of sighting.
Add a question mark to the end of a sentence to change the tone. For example, a simple statement like, "He didn't mean to kill her" goes from an expression of confidence in the individual to a question meant for interrogation: "He didn't mean to kill her?"