Break the assignment up into stages with a series of deadlines when successive parts of the project are due. For example, students might first submit a review of the literature, then a statement of the research question and design, then the findings, then the discussion. Respond to each part separately. At the end of the project students submit the revised whole, which will be much better and easier to grade than it would be if you saw the whole document only once, at project's end. Build in ways for students to help each other.
Students are good at keeping each other on track and suggesting improvements.
Peer groups can meet either during class or outside of class to read each other's drafts and respond to them. Peer critiquing of drafts, however, is just the most obvious way in which students can help each other. Students can collaborate at several stages of the process, from the time they first receive the assignment. They can help each other define their research problems, design their studies, and invent ideas for their discussions and conclusions. When trying out a new assignment, be flexible and supportive.