Visit a place that is similar to where your narrative takes place. For example, if you are writing a paragraph that occurs in a hospital, spend time there. Observe what people are wearing, saying to one another. Note how different areas of the hospital may smell differently.
Look at pictures of objects in your paragraph or depictions of environments that are like your setting. Sometimes it's difficult to visit what you're writing about. If, for example, you're writing about fishing boats, gather pictures of boats from the Internet or books. Look for online videos, too.
Make a list of as many details as possible. Include them in full sentences, if possible. For example, instead of writing down "tea stains on cup," formulate it into a complete thought: "Tea stains on the lip of the cup looked like brown tear drops."
Pick the details that help support the mood of the paragraph. For example, a paragraph that is meant to be mysterious and suspenseful, might mention shadows or eerie descriptions.
Write the paragraph, pulling details from the list as necessary. Write several drafts, using different details in different places. The act of writing the paragraph may help you come up with more useful details that aren't on the list.