Explain to your students what critical thinking is and ask them to give examples in their life of when it is necessary. Some examples might include when they have to make medical decisions for themselves or their families or when mediating an argument between their children.
Put your students in a group learning situation that requires the use of critical thinking skills. Divide students into two or more groups and assign them to research and argue one side of a complex topic such as global warming or religion in schools. This will teach them to offer their own ideas intelligently, listen to others' ideas and integrate the two.
Tell your students a story without an ending. This could be a short fiction story or a news story that they may not have heard about before. Have them discuss how the story might end and why they think it should end that way. After the discussion, tell them the real end of the story and have a second discussion.