Expand your field of vision.
Don't be so focused on the sky that you miss the ground. A person's kneecaps might be as defining as his nose. Look up, down, all around for the details that best capture the thing you are describing.

Circle your adverbs.
Watch for unnecessary, irrelevant or extraneous adverbs (especially the ones that end in "ly"). Examine your adverbs to make sure you aren't forcing them to do the hard work of observation for you. Instead of telling us that the heroine works "tirelessly," tells us about the callouses on her hands or her heavy walk.

Use adjectives in surprising ways. Try to write description that contains verbal surprises. Seemingly unrelated verbal combinations—"frightful goodness," "ferocious necklace," "barnlike body"—can strike exactly the descriptive note you want.

Don't use unusual adjectives twice.
Common adjectives like "small," "brown," or "wet" can be repeated in a story without drawing attention to themselves. Less common adjectives, like "lissome" or "sinister," should only be used once per story.