People need a reason to work as a team, and that reason is a common goal. 

Common goals create shared purpose. Individuals become motivated to work together as a team to accomplish the goal. 

Research shows that common goals - 

• Help bond the team 
• Focus attention 

You have to manage the various agendas  

• Personal agendas - people act in their self interest (ex. "I want that promotion") 
• Competing agendas - personal agendas often conflict (ex. everyone wants the credit and no ones the blame) 
• Hidden agendas - people often conceal their desires 
• Common agendas - an outcome that benefits everyone 

 How to set common goals (agendas)

• Clarify what's expected of the team  
• Use trust to expose hidden agendas 
• Expose and diffuse competing agendas 
• Focus on daily process goals 
• Propose win/win outcomes