Make an overhead of the writing sample and mark it with students' comments during class.
Role-play a student who is eager to hear a critique of their writing. Then have students pose as a workshop group whose job it is to inform you of how your paper could be improved. Encourage students to give specific and constructive criticism that will help you, as a writer, improve your piece.
Arrange students in groups. Have students critique another writing sample. Then, have them present their critique to the class.