Set deadlines for drafts; devote one whole team meeting to responses/revision of drafts.
Develop, as a team, a series of questions for each reader to ask about other writers' drafts; decide, as a team, what you want to look for in each writer's draft
Before distributing drafts to the team, each writer should provide a cover letter with the draft, explaining what she/he tried to accomplish, pointing out strengths/weaknesses, and asking readers specific questions about problem areas.
Write back to each writer and be prepared to discuss your responses. Provide both positive and negative feedback to writers. Be descriptive, pointing to particular sections or sentences, providing suggestions for revision and explanations of those changes.