The coach must have a clear voice, and a command over the English language. Many coaches are great players, and understand the game extremely well, yet are completely ineffectual as coaches due to their inablility to pass their knowledge onto the team. Coaches must be able to relate to players as individuals, as well as to the team as a whole. They must be able to communicate with the parents of their players so that expectations are clear, and that team and individual goals are clearly understood. This is the easiest way to gain the respect of the team, and the parents.
Personal appearance is important.
Be on time. Be fit, not excessively overweight. Keep your mouth clean, no obscenities. Be committed to the team. It is often an art form, and almost always demands creativity.