Treat others the way you want to be treated.
Lead by example.
The first was drilled into me by my mother that was raised as a church going midwesterner. The second came from Boy Scouts but has been reaffirmed throughout my life through observation of others and seeing the results of doing what I feel is right. These are the two lessons I try to instill in my children and the children I coach. If I had to choose a third it would be "only you are responsible for you happiness and success" but that lesson takes some shit experiences to really internalize.