Even if you cite your work correctly, you need to be aware of how not to plagiarize. The Council of Writing Program Administrators has prepared a definition of plagiarism:
In an instructional setting, plagiarism occurs when a writer deliberately uses someone else’s language, ideas, or other original (not common-knowledge) material without acknowledging its source.
Defending and Avoiding Plagiarism: The WPA Statement on Best Practices. Council of Writing Program Administrators. Retrieved August 6, 2015