Setup for World without Adjectives
Photocopy (and make a transparency of) copies of a passage you have selected and omitted all descriptive detail. Tif used a passage from detective novel that describes an investigator arriving at a crime scene -- and without supporting description, it's pretty bland rather than grisly. Other passages work well (I used Michael Chabon's Mysteries of Pittsburgh, a passage that reveals a great deal about a character unless the description is removed) and a pulp romance would work really well. Have them decide where they think detail should be added and what they would add and let them rewrite the passage.
When they are finished, ask volunteers to read, or collect and randomly read a few passages. Discuss to see where people generally agreed detail need to be added and what was lost to the meaning and effect of the passage without it. The pass out copies of the original passage (and maybe make a transparency) to show them what it really looked like. Discuss the difference between the two, and impress upon them that this is exactly why detail will be so important in their essays.