Show your reader what you are trying to describe instead of telling them directly. For example, instead of writing "There was a dog in the alley," write, "The seething dog stalked the length of the dark alley." The use of active verbs, adjectives and precise language will make your writing more engaging.
Use literary devices, such as similes and metaphors, to give the reader a point of comparison to what you are trying to describe.
When trying to describe something, think about all five of your senses and how they react to the object, person or place that you are trying to describe. Even if those senses don't directly relate, they can still be useful by describing what is around your subject.