If I had to pick a single ingredient it is that I set the example of how people should work and interact. A team will be successful if everyone feels a part of the team and knows the boss is right there working just as hard or harder. It may be different work than they are doing, but the boss must be visible and interact with the other team members. Setting the example of how to deal with clients, vendors, and peers. Asking questions and listening to answers. Engaging people in a group discussion and being approachable. And giving helpful advice when called for.
That is what builds trust, respect, and a team feeling. "Do as I do" works much better than "Do as I say". Excellence starts at the top.