According to the Human Synergistics organization in their team-building research and training, several interpersonal skills are needed by team members in order for teams to be effective. They are:  

Listening and clarifying: requires that team members pay attention and be responsive to the direction taken by the person talking. Do not interrupt the speaker and do not judge what was said. Concentrate on summarizing and understanding what was said.

Supporting: involves encouraging people to speak up and creating a positive climate where others will feel free to offer ideas. They are not defensive, afraid of repercussions or ridicule. A positive climate is created by truly believing in the fact that everyone is important and can make a contribution to the team. Everyone is treated with respect and all ideas are considered. Focus on what is right with a comment, not what is wrong.

Differing and confronting skills: Ability to present conflicting ideas to the group without threatening anyone. Focus on factual issues and avoid discussing personalities.

Quality as a personal commitment: A commitment to excellence is essential. Team members must accept their responsibilities, be willing to do quality work and be willing to pay attention to details.

Acceptance: Each team member brings a potentially valuable mix of skills to the team. Unless each member is valued as an individual there will be a reluctance to accept one another's ideas and contributions.

Feedback: Open and honest communication is critical to achieving results. It must be done in a positive and non-threatening way, concentrating on facts and the issue at hand.