Many of the strategies you can use to enhance the abilities of students to read expository texts are similar to the strategies you use to teach them how to write those texts. In other words, you should have them go through the text and identify the communicative elements of the text, including speaker, audience, and message. Next, you should look for a thesis and supporting arguments.
A good in class activity is to role play the back-story to recreate the rhetorical situation that might have elicited the exposition. Another good exercise is to have students retell the information but to different audiences, and to recast the exposition in narrative or visual form.