Talk to your students about the importance of academic honesty at the beginning of the semester. Tell them that they must submit original work, and that cheating will not be tolerated. Make sure they are aware of what constitutes cheating and what doesn't. Be clear about what actions will be taken if standards are not followed.
Help your students when they struggle with the material. Some students may resort to cheating if they do not understand what they are learning. Learn to recognize when your students are struggling, then you can prevent them from cheating. For example, you can offer to help them with the material after class or encourage them to see a tutor.
Ask your students to submit their first drafts. In addition to providing feedback about their writing, you can also make sure they did not accidentally plagiarize. Sometimes students become confused about what constitutes plagiarism. For example, they may paraphrase instead of writing in their own words. If a student accidentally plagiarizes, you must correct him right away.
Speak to a student in private if you catch her cheating. Calmly inform her that you noticed her cheating on an assignment. For example, you can say, "When I was grading your research paper, I noticed that you did not give credit to any of your sources." After you inform her of her wrongdoing, listen to her side of the story. Use your own judgment to determine if your student knowingly cheated or did it by accident.