Give specific instructions about what kinds of sources students should use and how to cite them properly as part of your assignment. Offer resources for looking up proper citation format as well as resources on how to distinguish among sources.
Provide feedback that shows students that someone has read the work and looked at the bibliography or works cited page. A common belief among students is that research papers are not read.
Let students know that you will check some online sources from selected bibliographies using a commercial search engine such as Google or Yahoo or a plagiarism detection software such as Turnitin.