Assign students distinct perspectives for observing an object or place. For instance, if you tell a student to "be the eye" of the viewer, that student is allowed to describe things only in terms of visual facts. If you assign someone the role of ear, that student is allowed to describe things only through sound.
Give students time to observe where they are or what they're experiencing in terms of their roles. Five minutes or so should be enough.
Have the students write their observations according to the roles they were given. Even as they recount their experience through the metaphor of their roles, this exercise teaches students to think and explain in terms of fact and hard descriptions. The method helps studens focus on what can be experienced and written as fact, rather than using vague language for their expository writing.