Collaborative learning can be a powerful teaching tool but group work must be designed carefully to be effective and inclusive. Always keep in mind the five key elements that differentiate effective collaborative learning from simply putting students into groups: Positive Interdependence, Individual Accountability, Face-to-face (Promotive) Interaction, Interpersonal and Small Group Social Skills, and Group Processing. Ensuring that these elements are implemented can be the difference between transformative group experiences and loud student complaints. Some suggestions for effective group work:

Be clear about the expectations for the group and for each individual. Allocate tasks to be done and be sure that each person knows what he or she is to do and what the deadlines are.
Be sure that everyone contributes to the discussions and tasks. If appropriate, assign students different roles (e.g., chair, scribe, authority) and vary these roles at each group meeting.
Have clear criteria for assessment. If students will be evaluating each other, define different levels of performance for different criteria in a rubric so everyone is on the same page.
Discuss with students why you are having them work together and how the group can promote their learning.
Provide students with tools to improve their team-building skills (see links below).

One factor that many instructors fail to consider is the possible equity implications when you ask students to work in groups outside of class. Students who are working in off-campus jobs, or caring for others in their household, may have significantly more trouble attending group meetings, which their peers may hold against them in group assessments. If you are going to ask students to work on projects in groups, be sure to provide some time during the class session for the groups to meet, and encourage them to keep out-of-class activities asynchronous.

See the following links for additional guidance:

An Overview of Cooperative Learning
– an introduction to the many forms of collaborative and cooperative learning, including short-term versus long-term projects and the key elements of successful groups
SERC Pedagogy in Action module on cooperative learning– provides specific suggestions for implementation
“Three Pillars of Cooperative Learning – Positive Interdependence, Individual Accountability, Promotive Interaction”
Guide for Working in Groups from Derek Bok Center for Teaching and Learning (Harvard) – “A Note to Faculty and a Quick Guide for Students”
- The section on “how people function in groups” could be particularly useful for developing students’ team skills – have students identify the roles they tend to take on and then discuss how they will fill in any roles that are missing
"Successful Strategies for Teams: Team Member Handbook" - A handbook written for students by Linda Nilson and Frances Kennedy provides tools to help students determine their own strengths and weaknesses as team members, as well as navigate team dynamics and organize team activities. The tool templates referred to throughout the Handbook are available in this Excel file.
Journal of Excellence in College Teaching special focus issue on “Small-Group Learning in Higher Education—Cooperative, Collaborative, Problem-Based, and Team-Based Learning”
Carnegie Mellon’s Eberly Center has a great collection of group project tools (e.g., contracts, assessments, evaluation forms, etc.).
This Faculty Focus article has some good suggestions for the reporting out process after students have worked in groups.