1) Choose a setting. You might like to browse some photos of architecture or landscapes for inspiration.
2) Imagine what it would be like to visit that place. What might you experience there? How would each of your senses respond? Jot down a few ideas in neutral, objective tones. For example, a beach scene might include notes like "low tide, sunny, dead fish, seashells, light brown sand."
3) Write a detailed paragraph describing the place in negative terms. Include at least five specific details. Use sensory input and word choice to make the setting seem unpleasant. Try to influence the reader to feel sad, wary, angry, or other dark emotions. The beach scene might now begin: "Hot sun baked the beach to crumbly grit. The receding waves left a single dessicated mackerel reeking near the high-tide line."
4) Revisit the same setting, but this time describe it in positive terms. At least three of the details should be ones from Step #3 above, rendered in a fresh light; the other two may be different ones. Tune the sense imagery and vocabulary to help readers experience happiness, anticipation, excitement, or other bright emotions. The new beach scene might start like: "Sunlight warmed the beach as the tide went out, relaxed waves lolling against the sand. Two fiddler crabs waved to each other as they shared a plump mackerel that had washed ashore."
5) Add a character to the scene described in Step #3 above. Spend a paragraph or two explaining what this person is doing there and what they experience. Repeat this step with the scene from Step #4.
6) You can stop here if you wish, but if you're getting good results from one or the other example, by all means continue. For extra credit, have the two characters meet each other, and try to figure out how to juxtapose their opposed experiences!