Most of my students seem to be strugling with the research proposal stage and as such they resort to plagiarism. this is an indicator that they might be having difficulty in translating what they have learnt into practice.
By reading some good books, review articles, knowing current status of research about their topic... But most important they need to be focused in approach regarding the problem and hypothesis of their study, for which proper review related to their topic is necessary....
students are indulging in plagiarism because research may be just a formality for them..they themselves have not taken up problems of research seriously to be explored...a better way is to let them decide a topic that they feel is their observation...after all any research starts with an observation..let them see if there is something that they would like to know about in depth..ask them questions about what explanation they think is possible for that...and then encourage them to search the answer in literature, and if they find some interesting theory (again according to what they feel is best/justified) let them think about it in details, raise more questions about it and see for themselves how much answer they have found for that in literature...they will themselves come up with some hypothesis to be tested and would be able to carry the process further with INTEREST and CONFIDENCE... :)
The tension between theory and practice arises not because theory, in itself, is inappropriate. Experience or practice alone can only speak about the concrete, individual cases that it has encountered. Theory alone, on the other hand, is apt to fall into impractical rabbit holes. You may let them do a research based on what they have learned into practice wherein they have some questions and teach them how to look for an answer in literature justified by the existing theories.