I did this one yesterday and had a good result. From Western Wind, an Introduction to Poetry by David Mason and John Frederick Nims. Write a descriptive poem (of, say, a dozen lines) about a familiar object or anything of interest to you. Do not use any adjectives until the last line; then try to use, effectively, a series of three. Here’s a famous example from Charles Simic.

Fork – by Charles Simic

This strange thing must have crept
Right out of hell.
It resembles a bird’s foot
Worn around the cannibal’s neck.

As you hold it in your hand,
As you stab with it into a piece of meat,
It is possible to imagine the rest of the bird:
Its head which like your fist
Is large, bald, beakless, and blind.