The “Soccer Player’s Creed” is a great foundation for setting expectations and rules for a team. The original is from a website called Coaching American Soccer though I’ve made a couple changes (in blue).
Soccer Player's Creed
I will know where the ball is at all times and never turn my back to the ball.
I will keep my eyes on the ball, in bounds and out.
I will never make a preventable throw-in error.
I will always keep intelligent communication flowing between myself and my teammates.
I will always talk with my coach when I have a concern.
I will never put down a teammate.
I will never incite an opponent or be affected by an opponent’s “trash” talk.
I will never kick a ball out of bounds on a corner kick.
I will constantly move properly according to the flow of play.
I will always set up passing opportunities unless I have a better dribbling or shooting chance myself.
I will always know where opponents are when receiving a pass and never let the ball be “stolen.”
I will strive to get the “big picture” at all times and know what all players are doing.
I will strive to play hard and aggressively, giving 100% at all times, but not commit “stupid” fouls.
I will know what my options are with the ball before I receive it.
I will consistently move to the position that will best benefit my team.
I will never retaliate or show dissent after being fouled.
I will keep my vision on the ball during the performance of ball skills.
I will listen to my opponents to obtain strategic and tactical information.
I will never allow my opponents to do anything uncontested.
I will never anticipate a referee’s call. I will not stop playing until I hear the referee’s whistle.
I will never agonize over my mistakes, I will learn from them.
I will always play as part of the team.
I will know all the Laws of the Game and how they are applied.
I will honor the game, demonstrating fair play and sportsmanlike behavior both on and off the field.
Please feel free to comment with any additions or edits you’d recommend.