Think of your team as a class, the practice as a classsroom, and the coach as the teacher. Parents can support their children by supporting the teacher. And you can't have one or two coaches at practices and twenty at the games. Make sure parents understand the team rules regarding sideline behavior, respect for referees, coaches and opposing players and that they behave accordingly.
Lead by Example.
If coaches remain calm, players will follow. If coaches are negative, the team will be too, reducing the opportunity to learn in a positive, supportive environment.
Focus on Growth not the Results.
The most important measuring device for a coach is in the team's ability to progress, both individually and as a team. Different kids progress at different rates, and abilities rise and fall as they mature physically and mentally. If there is continued focus on the development and progression of the team and players, the wins and results take care of themselves.
Let Players Dictate Their Level of Competition.
Create opportunities where players can dictate their willingness to compete. Build time into practice where players can play without constant structure and instruction.
Be Respectful to the Referees.
As the teacher, players and their parents will respond to the way you deal with referees. Hold yourself to a high standard. Many referees at the youth level are learning and need positive reinforcement to maintain their interest in the sport.