The best way to "get parents on board" is to hold a preseason parent meeting and explain the following points to them. Since it is best to provide to them in writing, you should consider creating a "parent handbook."
Review expectations for behavior of parents, players, and fans (only the coach should talk to the players and officials during games)
Communicate team rules and personal rules
Review seasonal expectations for team
Review policy for absences from practices and games- for example: playing time issues in regards to attending practices
Drop-off and pick-up procedures
Review what you will do if a child is not picked up
Game and practice schedule- season calendar (include any special events or post season dinner/award banquet)
Phone number that parents can call in case of inclement weather, or what the plan is for inclement weather
Emergency phone numbers for you, closest hospital/ER (where you will take someone who is injured)
Code of Conduct for parents and players to sign
List of what each player needs for every practice and game
What to do if it rains on game day
Review the best way to get in touch with you if a parent has an issue he or she would like to discuss and how you will contact them. Right after practice or a game is not seen as an acceptable time; communication through evening phone calls or e-mails will prevent you from being bombarded by parents.