One clear-cut way to help students understand their responsibilities to a course, its content, their classmates and to the instructor, is to create a simple Course Contract. Such a document should include both student behaviors, rights and responsibilities as well as those that can be expected of the instructor. Many faculty members ask students to write the contract, stating their expectations (this is a good group project); the faculty member then adds any obvious omissions. Having students participate in the creation of the contract encourages buy-in to the concepts.
For online courses, the instructor might ask students to create items that specify the frequency and nature of their online interaction with course materials and peers. If using online groups, it is especially important to have student identify expectations for group participation.