It builds itself. What you CAN do, however, is create the environment for the team to flourish and assemble itself. Team members must share a vision. Team members must value a win for the team more than they do a win for themselves. Keep your teams as small as possible.
Big teams are difficult to lead and have more problems communicating a shared vision.
Teams must be able to think and act fast. Everyone on the team must be able to offer input, ideas, and criticisms. Nothing must be held back for fear of reprisals. Teams that learn the most will lead the most. Your teams must stay aware of the latest information, techniques, and technology.