Depending on the level of detail that might be useful for each assignment, have students write out a paragraph or a page of summary for each assigned reading. When collected in a reading journal or learning log, these summaries help students understand readings more fully when they are first assigned and remember them clearly for later tests or synthesis assignments.
You might also consider asking students to do more focused summaries. By providing key questions about the reading, you can help students narrow in on the main ideas you want them to emphasize and remember from a reading.
Or if abstracts are significant in your discipline, you might ask students to analyze the abstracts in a major professional journal and write similar abstracts of the readings they are assigned in the course.