Most every move you make as a leader influences teamwork. 

Things we do that divide teams  

• Over reliance on company goals - people respond better to shorter term goals that reflect the work they actually do together 
• Implying team standards - if you don't clearly define "teamwork" under different circumstances your team can't hold one another accountable 
• Showing favoritism - your "favorites" are divided from the rest of the team 
• Discouraging venting - research shows that a good old fashion b*tch session is actually an effective bonding exercise 
• Allowing weak links - when you're too patient w/an under performer the team suffers 
• Ignoring bad behavior - bullying, harassment, rumors, gossip & discrimination tear a team apart