Dr. Renea Frey, Xavier's Writing Program Director and Assistant Professor in the English Department, has provided a useful and informative guide to maintaining academic integrity in your writing, including guidance for using quotations, paraphrasing a source, and summarizing a source. The guide also gives advice to help avoid plagiarism, to evaluate sources, and how to determine when citation is not necessary.
You can access the guide here: Citing Sources and Academic Integrity
In addition, the Xavier University Library has compiled and created a comprehensive XU.tutor! tutorial to help members of the Xavier community prevent plagiarism in their writing. The tutorial can be found here: Preventing Plagiarism
http://www.xavier.edu/library/xu-tutor/xu-tutor-Use.cfm Discusses the need for citation and the definitions of plagiarism.