Before you begin to write, sit down with a sheet of "descriptive spiders." Imagine or visualize the scene you are about to describe and fill in as many legs around each spider as you can. Note ideas for each of the senses until you have a complete sensory experience in mind.
You will probably have more ideas than you need, but that's a good thing. Pick two or three that are most important or tell something important about the scene. You definitely don't want to list everything you thought of, only the most important details.
For example, when describing a laundromat, you might mention the steamy air and the smell of detergent and bleach. If you are describing a classroom, you might mention seeing colorful children's art on the walls or the smell of chalk dust.
A few sensory details help the reader paint a mental picture of your scene. They also help your reader relate what you are describing to their own experience, which helps them imagine what you are describing more fully.