If someone else initiates a worth while team project that helps the group move towards its goals, lend a hand. Don't pitch in. Some jobs, like tying your shoe, are one-person jobs where good teamwork means doing them alone. Other jobs are just other people's responsibilities and we should just let them do them alone. Be the one who initiates an action that helps your group move towards a group goal.
Timing is everything.
Don't take initiative. If you're always the one who takes the lead in making group events happen, be sure to let others take the lead too. Sometimes, this means standing back and letting others figure things out. If you have a contribution to make to the group, speak up, now. Don't speak up.