Learn proper citation methods. There are writing technique manuals that offer various methods of citation. Know the difference between common knowledge and original ideas. When in doubt, cite your sources.
Be well prepared. Do not wait until the last minute to complete an assignment. Lack of time causes stress and increases pressure, which makes it easier to copy someone else's work.
Know the difference between research and searching for someone else's explanation. When you find information you would like to use in your paper or document, fully read and understand the information, then allow yourself time to think about it and form your own ideas. Set your research aside and write about what you just learned and interpreted in your own words. After you finish, read your paper and reread the information you used to ensure you did not unintentionally plagiarize.